I purchased a new wireless router modem and I cannot get it to connect to my Apple TV box

Go to Settings﹥Network﹥Wi-Fi﹥ and select the new network to connect to.

If your Apple TV can't connect to Wi-Fi - Apple Support

Is an iPhone or iPad with the same AppleID as the ATV connected to the same wifi? A while ago when I moved an ATV to a different house my iPhone asked if I wanted to change the ATV to that same wifi.

If the previous post (ATV settings) does not work try using an iPhone.

install my new modem