How can I split my router so I can use my doorbell camera?

Sounds like you probably want to name the 2.4Ghz and 5Ghz networks differently, so that you can assign the doorbell camera to the 2.4Ghz network. What gateway model do you have? With the dual band gateways, the easiest way to change your wifi network names is to download and install AT&T's Smart Home Manager from your app store (Apple App Store or Google Play). It's a free tool and can help you change your wifi network names, identify if there are issues with your service, allow you to run a speed test, determine if you have good Wi-Fi performance throughout your home, etc.