Factory reset

Ah right if you have access to a computer you can do it yourself

If you forgot the passcode on your iPhone, or your iPhone is disabled

video

How to re your iPhone if you forgot your passcode - Apple Support

or if you know your Apple ID password they can do it but I don't know about a charge.

Depends why you cannot do it yourself. If it is activation locked to someone else's Apple ID then they will not help.

Try this Restore your iPhone, iPad, or iPod to factory settings – Apple Support