In this case to proceed further need a model number of your modem so that we can assist you accordingly. But if its a single unit which is the combination of modem and router you can perform hard reset that will make the modem to default. After resetting the modem will go to default setup any custom settings will be removed so use the default network name and password to connect to your network.

Finally “Factory Reset” will help us to go back in enabling the Wi-Fi where you will be able to see the “Default Wi-Fi name and password” and connect to Wi-Fi.

If this doesn't work please share the model number of the modem so we can help you on it .