If the password showing on the modem's sticker is not allowing you to connect to the WiFi network then the WiFi password must have been changed. In this case you can either access the modem's page to edit the WiFi password or reset the modem to it's factory settings.
If the modem is a TPG supplied one then you can click here for some instructions on how you can do it.
In the event that it is not possible to use a wired connection, your last resort would be to reset the modem. Please keep in mind that resetting the modem will change the settings to its factory default. If the modem is a TPG supplied NBN modem then the modem should reconfigure itself after the reset. Else you will need to manually configure the modem to regain access to the internet.
Feel free to check our Community page for help or contact us here for assistance.