When the creed said Christ descended into hell, it did not refer to the hell we think of when we use the word hell. The word used in the original, ancient Greek form of the creed actually meant something closer to the idea of the underworld, where all the dead were. Before Christ, people did not go to heaven–only through Christ were the doors of heaven opened to the just. All the dead had be in another place, of course, the good as well as the evil. This is the place meant when the creed said Christ descended to hell.
Many people are bewildered to hear that Christ descended into hell, because they assume the word hell means what we commonly think it means. I was bewildered about this myself after I became a Catholic fifty years ago. What I presume what happened is that because of
such bewilderment the original Greek word in the original form of the creed is now translated as “dead” rather than “hell.” The translation of the word involved as “hell” is actually a poor translation, since the creed never meant “hell” as we now think of hell.