I didn't want this to turn into a thread about "how do I convince this person", but rather, how it should be done in general or should it be done.
The important thing to do is to make such people
think rather than try to
convince them by forceful argument. In any case, it's not going to happen overnight. You need to plant seeds of free-thought.
I think there were 2 initial ideas that led me to dismiss religious stories.
The first was the commonly held view that not all religions can be right, so why believe any of them.
The second idea was why would a truly loving and intelligent creator worry about whether or not you believed in him, or whether or not you subscribed to this religion or faction? Surely it is how you behave that is important. And you should behave the same way
whether or not there is a god or reward in an afterlife.
These ideas are not unique to me, of course, but I arrived at them by my own thought processes and without any attempts at persuasion, as many others undoubtedly have. But they are good ideas to plant seeds of free-thought in peoples minds.