Breaking the screen time habit

My son is about to be 3 and my husband recently introduced him to YouTube and being on the tablet. He knows how to play different games and find all kinds of videos on YouTube. I’m frustrated because I know he’s on it too much and I need to break him of it but I have no idea where to begin.

Does anyone have any suggestions? I really wish my husband hadn’t introduced him to this kind of stuff at all, I know it’s all hindsight now so no judgement please.