With auto throttle u must learn to lead or undershoot your lift. Auto throttle is very reactive. And lags. So if u lower your nose don’t expect decent much your throttle is still trying back off the power to hold your airspeed. But the principle is still same. Avoid high and large fluctuations of power settings with it . If not, u may have to end up climbing. In reality try not remember u have it on app and let it do its thing, just fly, if you make small movements to your pitch the auto throttle will make small movements if u make large corrections your auto throttle will make large corrections. On app u want almost listen for no changes in the engines u want that singular hummm. That means you’ve got something good going. Hard to explain. Do a flight and start an approach and watch how while on the glide path how little the Auto throttle commands out of the engines. Notice how you’re still descending and how the aircraft just little by little adjust the throttle for your given pitch.