Hi @chuusol,
As @uliwooly mentioned, the easiest way to reset your phone is to do a factory reset. Go to Settings > System > Advanced > Reset options > Erase all data (factory reset).
If you can't access the settings menu, try performing a software repair using a computer and Xperia Companion. Keep in mind that you might have to start the repair with the phone unplugged and check the box next to the text "My device cannot be detected or started, or is a Smartwatch 3".
I hope that helped!
