How to unlock passcode on iPhone 6 plus?

My dad found a iPhone 6 plus & it's from T-Mobile and right now it's not in service and It has a passcode but we both don't know how to unlock it. But we don't have access to a computer. So is there any way to factory reset with no computer?

If you can't unlock it with the passcode then the only way to reset it is by plugging it into a PC with iTunes.

You can visit the apple store and have a "genius" help you.

No, you can't reset it anyways because it will be icloud locked

The only way to regain an entry into your iPhone is to restore it. Yes, that's going to delete all data but, incidentally, even when you are locked out of your iPhone, you can backup data from it.

No there isn't & even if there was you'd still have to get past iCloud Activation Lock (you can't)