Wi-Fi connection to Android TV Box

2.4GHz or 5GHz?

It is 2.4Ghz

Then assign a separate SSID to the Guest Network, which is 2.4GHz, and point any of your 2.4GHz devices to it. Any 5GHz devices will be pointed to the SSID name of the 5GHz channel.

Is this easy to do.  Also I tried connecting with 5 GHz and it does not recognize that as well. 

Thanks for your help

Pretty much. I don't think you mention what equipment you have.

I have BGW320-500 fiber router. 

There are instructions around here on how to do that with the gateways. I don't have the link because I don't use AT&T internet services and don't want to steer you wrong but it's not hard to find.

2.4 GHz has a different SSID than 5Ghz one. I guess, it was different from the beginning. 

Ok. So point the 2.4GHz device to that SSID and pw (if different than the 5GHz radio).

The device I am having trouble connecting an Android TV box supports both 2.4 and 5Ghz.  So not sure how I can separate these channels on the Android box.

Thanks