find my offline iphone12

My son got a new iphone but has lost it before he could set up find my phone etc. We have tried find my iphone (offline etc) but cant find it because its offline. We have tried calling it, its ringing so its still on but we think its somewhere that is closed for the weekend. I have spent all day trying to work out how to find where it is with no luck, does anyone have a fix? thanks so much for any help