Last Channel

When I double click the play/pause button on my Harmony Hub remote it sometimes bugs the Channels app on my Firestick 4K and it restarts.

I want to program a dedicated button for the Hub. Problem is the "BACKSPACE" on the WINDOWS COMPUTER device in the hub isn't doing anything. The "P" for previous channel is working fine? Do any other keyboard shortcuts work for previous/last channel? Thanks in advance.

How about the google tv?