Dear

I appreciate your help in the following case that I describe:
I currently have a TP-LINK MOD router. WR641G / 642G v4 081520C2 and a TP-LINK MOD modem. td-8616 that are installed correctly and working perfectly with the internet.
My concern is the following, in what way should I configure these equipment so that I can access the router and modem and perform any configuration without having to disconnect the router from the router and connect it directly to the modem.
Currently I can only access the router and perform any type of configuration or revision, but I cannot access the modem.

Thank you