If you need to move a booked customer from one time slot to another, it's easy to do.
Navigate to the Experiences dashboard in the Shopify admin.
Select the time slot for which the customer is currently booked.
Click on the dropdown and choose "Transfer
Choose which booked line items, day, and time you'd like to reassign the order to
Your customers will be notified that they have been reassigned to a new time slot. Here's what that email looks like: