Question on Radio Frequencies

New to SimConnect. I’m attempting to build my own radio set. I can read the frequencies (Com1, 2, Nav1, 2) and get notified of a swap event.
However, I cannot figure out how to write the standby freqs. I understand the vars are not writable, but I see there are events for setting them,
But I can’t figure out how to use events for this. I’ve been playing with it for a week with no progress.
Can anyone direct me to something tutorial or manual that can help?
Thanks much!

I believe that Frequency entry is in BCD, not hex nor decimal