Disable submit button based on class availability

I am trying to stop users from registering for class when no slots are available. Records are added via an excel userform into a access table. The user selects a class from the combobox and submits. That works fine. I have query that tracks the number of slots available for each class. How can I tie both together to prevent the users from submitting the record when no slots is available? My vision was once a selection was made and no slots available for that class was to disable the submit button.

Thanks in advance.

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the combo box can have 2 columns from the query: ClassName, SlotsRemain
then:

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