Mandatory store meeting?

So my store had a mandatory store meeting my manager says ALL PARTNERS MUST ATTEND but its on a day I never have available and it's my only day off. I refuse to work 7 days a week What options do I have??!

Update: Thanks all for commenting. I'm trying not to sound too whiney or complainy, it's just I have burnout. Just to clarify I work 2 jobs do Sunday is my day off for both because I need one day a week recover and rest as well as catch up on groceries/cleaning etc. Im gonna try and book off the next couple of days after the meeting just so I can find some time to recharge. I didn't even know about it saying that in the employee handbook but to be fair its been over 5 years since I've looked at it. Cheers and thanks all for responding. Hope you're all doing well in these trying times!