Can not toggle btnm button from different button

I have been working on btnm buttons and I have a problem with to toggle from outside of btnm button.
I mean toggle btnm button to not touch btnm buttons.
To be clear:
I have a screen and one btnm button in the center and mapping 3 elements like {“A”,“B”,“C”,""}
and I have two different buttons on the left and right side of screen.
So I want to toggle any of btnm buttons using left or right buttons.
I have tried couple scenarios but did not worked for me.
Can you help.
Thanks

Please fill out the template. Questions that do not use the template are likely to be ignored (unless they provide the same information the template asks for).