Take off the drain cover or stopper. Remove any hair or gunk you can see (use gloves, a hook, or an old wire).
Pour 1/2 cup baking soda directly into the drain. Try to get it as far down as possible (a funnel helps). how to unclog shower drain with vinegar and baking soda
: Immediately cover the drain with a plug, a clean cloth, or a plate to contain the fizzing and direct the pressure downward. Take off the drain cover or stopper