@phil This only works if you are the owner of the router because when you go to the router's IP it requires a password and username. PartyGoer said that this is someone else's guest connection thus he cant do that.
@PartyGoer If you want the guest password you will most likely have to ask the network administrator (owner) for the passkey. You can also TRY to lookup the default login credentials for the specific router type then try those credentials on the page you get to when entering the router's internal IP in the address bar of your browser. Then you can navigate to the page and see what they set the guest password as.
*The second method I said is most likely illegal so I am simply saying it as information*