This would be on an ISP's supplied router, not your own router. If not there, is fallen off and u may have to get another router from ISP, or ask them how to reset to factory.
Not every router has a PIN / password printed on the label. If you know your router' configuration password (not the WiFi password), go to its configuration page, and change WiFi password (and remember it / write it down).
This would be on an ISP's supplied router, not your own router. If not there, is fallen off and u may have to get another router from ISP, or ask them how to reset to factory.