There are TWO p/w's being discussed here I think.
1) The WIRELESS password which it appears is known? Or was KNOWN at some point.
2) The ROUTER password to get into the Router and make changes. This appears to be the one NOT known as well?
In any event, you must get into the router and then you can change the Wireless p/w. Two ways to do this I would think, maybe three...
1) Using your normal browser got to the Routers IP Address, 192.168.x.0, where x depends on the Router setting/mfg. Possibly your Browser will KNOW the UID and PW and let you in.
2) If 1 fails, tell us the ROUTER MFG and we can probably tell you the DEFAULT USERID and PW it uses, and you can try that with #1 above.
3) Do the RESET and that will set the DEFAULT USERID and PW on the router, but we'll need to know the make and model of the router to determine the defaults.