If you still have to do training today, I’d say just inform the trainee that today you’re not feeling too hot and hope they’re understanding of it, as for the hours, for sure submit availability change and have a 1-1 discussion with your SM about it and explain that you won’t be able to healthily continue working the hours you have, if they don’t want to cooperate and you don’t want to quit, maybe submit for a transfer, maybe a different store will be more accommodating

I hope this helps, I know sb can be a pain and how difficult it is to work through some stuff but ultimately do what’s best for you