sky broadband router

Hi, hope everyone is staying safe during these mad times.   I have the original wired router provided by sky pre 2012.  I can't find the model number (it's nowhere on the router and the box is long gone) but have the serial number.  I need to change he security settings but don't have user name or password.  I have tried restoring factory settings but when I key admin inusername and password in password fields it does not work  Can anyone help please?