Your RCMO will have details of the Regular to Reserve transfer process. My understanding is it’s basically a paperwork signoff which makes your transition to the reserve seamless from the day after your termination date.
I did it. It was a single piece of paper that my CO signed and wrote a very kind statement. At the end of the day you have a skillset that the army won't want to lose, if like me, you are leaving because you and your situation has evolved, not because of a dishonourable discharge, then the army will not be keen to lose what you have. It is a very simple process and it was so positive for my mental health to do it.