Well, Jennifer, you can't. Father alone is able to do that. He has spread the cloak of blindness
on many, such that they will worship slewfoot. This may seem hard to you, but in the long run, it is for their own good.
If they don't know the truth, then they cannot commit the unpardonable sin.
If Father is willing, however, some can be made to see. One way that has worked for me in
the past is to matter-of-factly state something like "Oh yeah, I did think about the rapture in the past, but when I read
John 17:15, I then realized something must be wrong. So I began to study, and---etc." The key thing
is though, if you cause someone to doubt their belief and blindness, you MAY be out of Father's will. Think about it.
If you can get that far and still have them interested, you can find a bunch of info to use