My fiancé won’t stop yelling - need advice

My fiancé is a great dad but when our toddler is doing things that she’s not supposed to or when she’s throwing a tantrum he automatically resorts to yelling at her 😞 she doesn’t respond well to yelling, it escalates the whole situation, and I end up feeling super stressed out and upset because of how he reacted. He’s great when she’s behaving and she loves him and he loves her and they’re super sweet together, I just don’t know how to get through to him that he can’t just yell at her when she’s not listening. I’ve snapped a few times and ended up yelling and I’m not proud of that, but I always apologize to my daughter and make sure she understands that it wasn’t okay for me to yell at her. He never apologizes for yelling and usually ends up in a bad mood after and isn’t the nicest to be around - I just need tips or advice on how to get him to understand that the yelling needs to stop.