Number Fields and Equation Fields

Upon record creation, a certain number of credits (e.g. 4) are assigned. I am attempting to incorporate a new field and form that allows the manager to add additional credits to the record. However, the number field does not reset to zero after the form is submitted. I attempted to use a Form Rule to reset the field, but this caused issues with the equation. Another problem pertains to the equation, which I believe would be better explained through a brief video demonstration.

I’m hoping this can be done natively in Knack. If not, I’m open to custom code solutions