@georgiahawkeye-
Is your Xfinity sevice via an Xfinity box connected to an HDMI port on your TV?
If the Xfinity box supports CEC, you may just be able to press a button on the Xfinity remote and have the TV respond by switching to the Xfinity's input, similar to what you do with Roku.
Otherwise, use the Input/Source or similar button on your TV's remote to switch back to the correct input for Xfinity.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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Ultra 4850 | Ultra 4800 | Streaming Stick 4K+ 3821 | TCL Roku TV 43S245/C107X