I think the idea is that you e.g. have the joystick in a 50% forward position. Now you don’t want to push the joystick forward all the time, so you press the FTR button, move the joystick to the neutral position, and release the FTR button. While the joystick goes from +50% to 0%, the trim moves the opposite direction fom 0% to +50%. The end result is still a cyclic deflection of +50%.
So with this FTR implementation you press the button when you move back to the center after you have reached the desired attitude, and the trim automatically compensates your joystick movement.
It is different from the HPG H145 with the spring joystick setting, where you press the trim release button before changing the attitude of the helicopter, to override the Airbus SAS system.