In the CC Channel activity window right mouse click on the Talk Group number. That will decrement the priority until it get to L/O. If you Left mouse click on the Talk Group number it will increment the priority level and will move to "HIGH" and "HOLD."
In the same window, if you hit space bar when a Talk Group is active it will also place that TG into HOLD. If you hit the space bar again, it will clear the hold.
You can have multiple TGs on "High", but only one on "Hold."
If you hit space bar in FMP, that will mute the signal and FMP will not process signal. If you have the wrong window active and hit the space bar, you can accidentally mute the signal out of FMP. Fortunately, the activity bar at the top of the window will say "MUTE" if you do that.
Guess how I know that.