Tell them to read the Bible from start to finish unless they personally have terrible morals they always convert. One time one I was talking to didn't even get half way through Genesis and was like nope. The first step is to get them to stop Christianity. After that depending on the individual you can open them up to Satanism. Give it time tho rushing will scare people away your best bet is to get to know the individual and figure out what parts of Satanism suits them the most things that they would whole heartedly believe and trust in. Trust your gut and if it's truly something that needs to happen Father Satan will guide you.