Can't long in with admin password



I loaned the unit to a customer. They logged into the phone and changed the admin password and don’t remember what it was changed to. Is there a way to default the unit back to factory settings? The manual specifically says

“If the DP715 was previously locked by your local service provider, pressing the RESET button will only restart the unit. The device will not return to factory default setting”

Any way around this???
If it helps, I can log into the LAN address with the USER password…

Thanks in advance