When you move the Fire TV Stick 4K to a different TV, the remote control's Power Button and Volume /– Buttons may stop working. This is especially likely to occur if the TV is of a different brand.
Here is what you do to make the remote’s Power Button and Volume +/– Buttons work again:
Go to Settings.
Select Equipment Control.
Select Manage Equipment.
Select Change TV.
Follow the on-screen instructions.
During Step 6, the Fire Stick will detect and identify the brand of the TV (e.g. Toshiba) that the Fire Stick is connected to, and then set up the remote's Power Button and Volume Controls to match the detected TV.