Do a factory reset to change your phone back to its original state before the first time you turned it on.
If you’re passing your phone on to someone else or your phone has a persistent problem that cannot be solved, you can perform a factory reset (also called a hard reset). Factory reset is not a step to be taken lightly. It’ll permanently delete all your data and customized settings, and will remove any apps you’ve downloaded and installed. Be sure to back up any data and files you want to keep before you do a factory reset.