How to transfer ownership of an iPhone to Samsung user/how does a Samsung user claim the iPhone under their provider/What do you do if iPhone user has different provider then Samsung user and how to fix that?!

Hello, I am a iPhone user and my friend recently broke her Samsung a20. I offered to give my friend my old IPhone that I do not use anymore, I totally wiped the iPhone clean and its ready to set up. But I have no idea how that would work. First of all, how do I unregister the iPhone so I can give it to my friend. Also, how does my friend register the iPhone I give to them under themselves, so it is officially theirs and they would be able to make payments under their providers independently without going though my provider and having myself billed. And second of all, since my iPhone’s main provider is Verizon, and my friend’s provider for their Samsung is Metro, how would that work? What are the steps in making this exchange work properly, what do I have to do? Please be thorough and very detailed, thank you so much!