Press the Axis mode select button.
This switches to 5 axis mode(LED green)[if 4 axis mode is used the LED is red].
5 axis, this switch acts as trim control, 4 axis the switch acts as rudder control.
You can verify it with the Thrustmaster control software(don’t know the exact name, there is a download for the Hotas 4 somewhere) I’m at work so I don’t know the specific details sorry, but I had the same problem yesterday
[edit] My bad, the picture points to the led. Button 11 or Button 12 is what has to pressed once to trigger the axis mode.