cannot erase all settings from old Iphone 7;

Can someone help me? I have an old Iphone7 (without sim card) and I want to give that phone to a collegue for testing some software apps. When I started this Iphone I saw my Apple ID account and photos from icloud. I want to clear all content and settings but i got an error. I am not connected to internet so also nog connected to apple account.

I have another gsm which is connect to icloud etc.

Can I erase the entire iphone without connected ?