You can easily deny shift applications for any worker who applies to an available shift.
Just as if you were going to assign a shift, click on any open shift. You will see the option to "Assign" a shift to the appropriate staff member, and also the option to "Deny shift application" by clicking on the trashcan icon:
You will prompted to confirm that you would like to deny the shift application, and must confirm:
Once confirmed, the worker will receive a notification letting them know they were not assigned to the shift:
If you'd like to learn more about setting up shift applications, take a look at this Help Center Article.