The Reverend Jim is correct. You need to access the admin web page on the router, which means you need to directly connect your computer to it with an ethernet cable since you don't have WiFi access. There, you can either view the password, or if it is obscured, you can reset it.
If you reset the admin password and forgot that also, you may have to do a hard reset (there is a recessed button on most routers to do that) and set it up again. Most of the time, the default admin password is either empty, or simply "admin" without the quotes.