Cannot deselect a time slot when full

How do I deselect a time slot when the slot is full? I need to edit some submissions but cannot get that done.

When the slot is already full then it will be automatically disabled so you will not be able to select or deselect that option. 

The options to have a full option available will be to add more items to the single option so if you have 10 and they are all selected then you could add 1 more so the slot is available again, the other option is deleting the submission, that will free up the option and you will be able to select it again. 

I hope this helps.