Reset pre-paid iPhone for little brother
I’m wanting to reset the older model iPhone that my kiddo has been using effortlessly for the past two years on the $300 prepaid plan so it can now be used by little brother as his first phone (his new Apple ID, his apps, etc). And I want to be sure I follow the right steps so that the number and pre-paid plan stay with the phone and I don’t break it accidentally when I reset. Would be grateful if someone can point me in the right direction on how to do that. Thanks!