wipe iphone6

A friend gave me her old Apple iPhone 6. Not exactly sure which version it is as I can't go into settings to see. Unfortunately, when I went to AT&T to connect the phone line they said they can't touch my phone due to Covid restrictions. My friend doesn't remember her code to access her old phone. I'm trying to wipe it to gain access as now it's hooked up w/ a phone number and service. Currently have no phone as I'm recently divorced and our family one got turned off abruptly. Any advice how I can regain access to this iPhone?? Please and thank you:)

Kim