There is a button on the left side of the yoke that is supposed to control electric rudder trimming and elevator trimming. When I hover with the mouse on this button a left/right wheel arrows and a hand-finger appear. However I get no effect at all when I click or when I turn the mous wheel.

Any idea what is the problem?  

Note 1: I can trim by binding a joystick/axis to the trimming function, but my question is specifically  about the physical button on the yoke

Note 2: The switch trim on the overhead panel is on

Same for me, in the end just did what you did, bound them to a joystick function. Was surprised there wasn't more about it on the web, must affect others?

Press and hold left mouse button and drag left or right.

2 hours ago, ambeat said:

Press and hold left mouse button and drag left or right.

This doesn't work for me