Check out the bottom of your router and find the network key. The multidigit long number is your WiFi password. Please try the network key a few times, as it's easy to make a mistake at first with the numerous digits.
In case the number does not work, or you have a Mesh Box system in your flat, the password is "welcometohomefully".
If this doesn't apply or help, just ask your flatmates. They have their devices connected for sure and can tell you the password 🙌