New semester but my classes have had new students added to the rosters

Hi everyone, I am a first year high school general music teacher for context. I got my rosters for the new semester today and I have a lot of the same kids but also many new kids added on. How am I supposed to teach my content to kids who have already missed over half of the school year in my class? Any advice could be helpful. Every time I feel like I have settled in and found a groove, my school throws me another crazy curveball and it feels like the world is going to end.