Having issues speaking up

So recently my parents, dad and step mom, have been trying to get me to talk louder and be more assertive, because at some point when I was a kid kid I had zero volume control and, often being told I need to be quieter bc I literally yelled without realizing it, accidentally made myself talk quiet af and idk how to break that habit, and I also wanna know how to actually get out of the whole "don't say anything and it'll go away" mindset and actually start speaking up about stuff again