The IP address wont indicate what the username/password is. If the credentials were not changed/configured, look up the default credentials for the specific device model on google, you should be able to find them. (usually something like admin/admin or admin/pass)
If someone installed this router, they likely changed the credentials and you will need to obtain them. If you don't know the credentials, there may be a guide online for bypassing/changing the password if you are local to the device. If not you will have to factory default the router and reconfigure.