Company issued phone, turned in with unknown passcode

1. Is this your corporate iPhone? Then please contact the system administrator of your corporate
2. If it is your personal device, in that case, do you have any profile installed by your corporate/organisation/enterprise/School Management?
   1. Erase the profile added by you If you have installed a profile on your own --> Install or remove configuration profiles on iPhone - Apple ...
   2. Or please contact the system administrator of the organisation who provided the profile to you

If you have a model that has a home button, you can press the volume buttons at the same time as the Home Button for several seconds without releasing will start the forced reset of the phone (I believe it asks you first)

I dislike iPhones without the home button, so if you have the recent iPhone model that does not have a home button, I'm not sure how to reset that. Maybe someone else can chime in.