How to make 5g gateway split to 2g and 5g as i have a 4g printer that wont connect.

Yes… When I switched to Tmobile, I just set up the 2.4 Ghz and 5Ghz bands with the same user name and Passwords that were used previously with Xfinity. I then did not have to to anything but unplug the Xfinity gateway and plug the TMOBILE Gateway in to get everything to work. 

Hey Pattycake, What allanl3561 was saying was that there is a way to separate the 2.4 and 5 GHz. You don’t have to continue to use your old router. When you are setting up a new wifi equipment, you can use the same network names and passwords that you had with the previous internet provider. Once you complete the setup, all of your devices will already know the network name and password, so you don't have to go through the wifi connection on each device. My husband set up the internet for our house, his parents’, and his sister all with the same network name and password. Now any time we visit each other, our devices seamlessly connect and we don't have to ask everyone for their wifi password.  

We offer the instructions on how to separate the wifi networks and name them in our support pages. https://www.t-mobile.com/support/tutorials/device/t-mobile/nokia-5g21-gateway

Hope this helps!