Key Binding does not seem to work for me - Comms and Nav

Dear Community, I found it hard to set the comms or nav frequency using my mouse. I want to press a key and add the frequency manually using my keyboard. When I look up key bindings in General Controls of my keyboard, I find it is bound to C for setting the comms frequency or N for setting the nav frequency. However, when I press and of those keys nothing happens. What is it I do wrong? Many thanks!