Navigate to the workshop and access the "users/candidates" section. Click the "edit" option next to each user.
Upon selecting "edit" for each user, you'll have the option to adjust their selections. Once you've removed the unnecessary dates for all users enrolled to the workshop, you can then proceed to update the workshop settings accordingly.
It's important to note that if any user is enrolled on a date you're attempting to deselect, the system will not permit you to exclude that date from the workshop setting.