On the Catering Menu page for that date, open Select Meals For this day and check or uncheck the meal(s) you want on the menu — each toggle saves (or removes) that meal for that delivery date immediately, so there's no separate save step.

To remove every meal from that date at once, click the Clear Menu button instead. You'll be asked to confirm ("Are you sure you want to clear the meals selected for this day?"); once you confirm, every meal on that date's catering menu is removed in one action. There's no undo, so if you clear the wrong day you'll need to re-add meals manually or re-clone them from another date.