the username and password are set in the 8600. You did that,
The hostname or ip address depends on if you have set it static or use DHCP.
In both cases that’s almost at the same place as the user and the pass.
Reading the owners manual for the R8600 will answer all your questions. At some point, it really is worth doing even though it is a lot of information to digest – reading the manual effectively increases the value of the radio.
Anyway, for the answer you seek, you just have to go through the menus on the radio and find and/or set these parameters.
Here is a setup guide I saw online. It assumes you have already connected the ethernet cord.