I’ve been there. I started the term afresh and spoke to the class about what had happened, what I’d noticed and acknowledged the role I played in that. I’ve them linked it into how that will impact their learning and why I’m concerned about it continuing. That’s then a springboard to explain my new, clear expectations that are all pretty simple - usually they can be boiled down to maximising learning through minimal disruption, which encompasses basically all behaviour. I created a new seating plan too, though these were the norm at my previous school.

Then I stick true to the expectations but really, really focus my attention on the kids doing well and doing the right thing (usually they have been the whole time anyway). This can be applied to the whole class too - It’s important to acknowledge when the class are doing the right thing. If possible, focus more on the positives than the negatives. It’s hard!

Good luck, it sucks, I will be honest that it’s happened to me twice early on - once I won them back, the other time I never did.

ETA - if your school has a behaviour management framework, use it and use it religiously. It will keep you consistent. Saved my butt when I was in your situation. If you don’t have one, make a clear escalation protocol for your class and explain it to them, then follow it.