I agree with what most say here; "they have to do it on there own,"
However, i've seen incredible ground covered in discussions between a non-believer and a believer when done in the epistemological way. Recommend reviewing Anthony Magnabosco on Youtube, he has some superb examples of how it's done...

I think you're right. As a kid I asked myself why are descriptions of heaven and Earth so similar to the sky and volcanic activity underground? Is that coincidence or an obvious sign that ancient people who didn't understand made it all up? You know the conclusion I reached. But to your point, when hell became BS I stopped fearing my inner thoughts and embraced everything about nature, which led to good thoughts about humanity and our place in the cosmos.

And how do you 'slowly chip away" belief in hell while he still believes in heaven?

ah, easy--Gehenna is on earth, a trash dump outside of Jerusalem, and our Norse/Angle scribes just had no better analogy than their understanding of punishment in an "afterlife," which btw is not even in Hades' (a Greek god) mythology.

The Bible--even a corrupted English version--is very clear, beginning with Samuel (accepted) to King Saul (rejected) you and your sons will be here with me, to the wisdom of Solomon, No one knows where they go when they die, All go to the same place, to various NT statements made by "Jesus," No one has ever gone up to heaven, The kingdom of heaven is within you, There is only One Immortal but i would caution you that all you will most likely do here is lose a friend ok.

There are other vv that really bring the deception home, Esau (whom Yah "had hated" ) giving up his birthright for a bowl of "red stew" that he was so hungry for he was "about to die," and then apparently inheriting anyway, as it was Jacob (you, basically) who was more or less forced to leave, and in the OT No son of man (which is how Jesus referred to Himself) may die for another's sins; the lifesoul that sins, dies, but i would keep that one to yourself for now.

Ppl who believe they are going up to heaven after they have died are in the Cult of Sol Invictus, descended from Mithraism (Apollos waters), but they are not going to appreciate being enlightened ok

About hell:

If they have kids, ask ‘em how bad they’d have to be for you to sentence them to eternal torture.

Virgin birth? Resurrection of the dead? Those sound just as far fetched to me. Probably more so as we have the here and now to compare it to.

Good luck with that!