How do I submit feedback on a service received in an Apple Shop?

A product feedback link will not get to the right people. Apple used to have a separate feedback link for sales, service, and support comments, but saw fit to remove it several years ago.

Best action is a well-written business letter. Phones calls get misdirected and those "While you were out..." slips for phone calls get lost or ignored, or numbers and names were improperly transcribed.

When I managed tech support in another industry, I preferred getting a letter regarding my employees' action, good or bad. I had a hard piece of data at reviews and the the letter could go in an employee's personnel file.

I'd go with the old fashioned way: call the manager of the store.

Ask for the name of the district manager.

you can try contacting apple Support ->  Get Support (apple.com)

and or give them feedback -> Product Feedback - Apple