Anyway I would like to suggest to the ISPConfig staff to focus this kind of problem in order to complete the good service that they offer to all the community.
Your problem is not ispconfig specific and nothing that could or has to be handled by ispconfig.
As Toucan pointed out, every router is different. So you have to take a look in the manual that comes with your router for detailed informtaion on how to install the router that you use in your network.
As you use a Dell router, go to the dell website, I'am sure they offer the manual for your router in their download section.