Make sure you are not in autothrottle mode - the throttles won´t "work" (can´t be moved by your hardware) while that autothrottle is controlling them. You must be in "manual throttle control" (autothrottle disengaged or even off) for the throttle to work. When you transfer control from the autothrottle to manual throttle (by disengaging it) you will see some "ghost throttle" symbology. Move your hardware throttle until it "matches" the ghost throttle - at that point the throttles will "snap
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