I need to change an appointment

This is a user to user forum and Apple is not here. You need to contact the store for help.

Then you need to call them. This is a user to user forum and Apple is not here. We can’t do anything about this.

Do you mean you need to change the time in your calendar app, but your phone is frozen?

If that is the case you can change calendar appointments synced with your iCloud online at icloud.com and adjust any appointments without needing to use your phone. If you use another calendar service you can also sign into those online as well.

I would recommend a hard restart on the phone if it is frozen https://support.apple.com/guide/iphone/force-restart-iphone-iph8903c3ee6/ios

I need to change an appointment at waterside shops in Naples Florida

I need to change my Genius Bar appointment at The Greene, Beavercreek, OH

Yes. I want to change my appointment today from 11:00 to 3:00.