The WiFi password can be accessed by logging directly into the modem. You can access the modem by using another device that is already connected to your WiFi and going to the URL 192.168.0.1 from the web browser.
The usernames and passwords vary depending on the type of modem you have. To find your model name, you can usually find it on the front of your modem.
Once logged in, navigate to the Wireless 2.4 GHz or Wireless 5 GHz tab to view or edit your wireless network name and/or password.