For anyone reading this in the future, if you are using the remote supplied with the XRS4900 (the BT-200 remote) and want to use the power, source and volume up or down buttons at the top of the remote to control your TV, you need to use the "Learning Remote Feature". Instructions are on the back of the remote but are quite hard to read.
You can also find the instructions here: https://buzztv.com/site/wp-content/uploads/2021/05/BuzzTV-BT-200-Remote-Manual.pdf