What can a christian mother of a 22 year old son who says he is transgender and having hormone therapy do to convince him to revert back to a male as this situation is tearing our family apart?

well, the best thing to do is not to convinve him. if he is happy with his decision, then he should have a supportive family behind him. but if his new switch is causing conflict, or physical, even emotional problems, then you, your son, and the rest of your family should compromise. talk about it. after you have told him about how you feel, things could run much more smoothly.

Your religion is irrelevant, there is nothing about Christianity that speaks against being trans.

Your childs is transgender, you cannot change them back because they were never the gender or sex they were assigned from birth - the doctor who told you the sex got it wrong, the gender you raised your child as was wrong. You accept that, you cannot change that and nor should you want to change your child. The problem here is not with your child but with you and your families prejudices - if you're Christian and you think of yourself as a good person then time to act like it, accept and love your child for who they are.