"He [Christ] descended into Hell." -- The Apostles' Creed
We need to consider (1) what (and/or where) is Hell
and
(2) why did He descend there and what did He do there?
As in much of the Bible, this also is a matter of "progressive Revelation". That is to say that often in the early part of the Bible less details is given on a topic; further in the Bible more details are provided until by the end of the Bible we have (in the Bible and in Christ) a full and complete Revelation of what God wants and believes that we need to know. And in the Church age He, by His Holy Spirit, guides us into understanding of that Word.
In the English language we have the word "hell" and traditionally it is used in the English language translations of the Bible. But originally the Old Testament was written in Hebrew and the New Testament in Greek. The words usually translated as "hell" are the Hebrew word sheol and the Greek word hades.
The concept of sheol is (some say) a shadowy existence or abode and state/condition of the "dead". Even in the Old Testament there is a clear distinction between the body and the soul. When people died, they (their souls) were gathered to their ancestors and they (their bodies) were buried (the grave). There are glimpses, as in Job where it is declared that though worms destroy the body "yet I shall see God".
The realm called "Sheol" in the Old Testament is called "Hades" in the New Testament.
Jesus the Christ gave us the clearest description of Hades as it existed even unto the time of His earthly Ministry. [St. Luke 16:19-31, AV]
19 There was a certain rich man, which was clothed in purple and fine linen, and fared sumptuously every day:
20 And there was a certain beggar named Lazarus, which was laid at his gate, full of sores,
21 And desiring to be fed with the crumbs which fell from the rich man's table: moreover the dogs came and licked his sores.
22 And it came to pass, that the beggar died, and was carried by the angels into Abraham's bosom: the rich man also died, and was buried;
23 And in hell he lift up his eyes, being in torments, and seeth Abraham afar off, and Lazarus in his bosom.
24 And he cried and said, Father Abraham, have mercy on me, and send Lazarus, that he may dip the tip of his finger in water, and cool my tongue; for I am tormented in this flame.
25 But Abraham said, Son, remember that thou in thy lifetime receivedst thy good things, and likewise Lazarus evil things: but now he is comforted, and thou art tormented.
26 And beside all this, between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence.
"the beggar died, and was carried by the angels into Abraham's bosom:" -- some, upon death, are "carried" or escorted by the angels to a place of bliss; a place of "Paradise".
"the rich man also died, and was buried; and in hell he lift up his eyes, being in torments" -- he died, his body was buried in the grave, but he was still very aware, very conscious. His "soul" was not "asleep" in the grave awaiting the resurrection "at the last day". Rather, he was in "torments".
They both were in the place or abode of the "dead" and they were able to see and communicate with each other. But the beggar was with Abraham in the "Paradise" portion of "hades", the rich man was in the "Torments" portion of "hades". There was "a great gulf fixed" between the two portions of hades and none could go from one to the other.
So, why do many think of "hades" (or "hell") just as a place of Torment? Perhaps one portion of Hades has been emptied; perhaps the Paradise portion, the place of bliss, has been transferred elsewhere and only the Torments portion remains.
Ephesians 4:8 -- He ascended on high and led captivity captive
First, He descended into Hades, to the Paradise portion where the Old Testament "saints" were awaiting the accomplishment of Christ's Atonement. He went there and proclaimed to them that Good News. Then He led them to Heaven itself; He transferred Paradise from Hades to Heaven.
Though Christ was fully God (fully Deity incarnate), He also, from the Incarnation, was fully human. So after He died (after He dismissed His spirit), He went to hades; His Body was laid in the tomb/grave.
Remember, Jesus was sinless. He bore our sins in His body on the Cross. When the work of Atonement was accomplished, He gave the Victor's shout of triumph "It is finished". Jesus was sinless. Jesus had paid the penalty for our sins. The penalty was paid.
As a human, He went to the "Paradise" portion of "hades" (the realm of the dead) just as the other Old Testament saints did.
As Deity Incarnate, while there He proclaimed the Atonement which He had acomplished on Calvary; the Atonement which set them free from that place of waiting. He led them from there to Heaven itself; He transferred "Paradise" from "Hades" to "Heaven".
Therefore, the only part that remains in "Hades" is "Torments". Were or are any of the inhabitants of "Torments" able to leave there to return to Earth or go to Heaven?
We trust in the Mercies of God Who 'is not willing that any should perish'.
But we should never presume upon His Mercies, for we are told of the 'finally impenitent'.
We are told 'Behold, now is the accepted time; now is the day of Salvation'.
In St. Luke 16 we read of the man who found himself "in torments". Then he wanted God's Salvation.
But, could he return to Earth? Or could he cross over to the place of "Paradise". Luke 16:26 -- cannot
It certainly seems he had opportunities in this life. He was not "ready".
It is 'appointed ... once to die and then the judgement'.