I am trying to use the frm_after_update_entry to update a field in a data form after a public form is submitted (for reducing the number of tickets available to a specific performance.

The documentation linked above includes examples that deal with user ids and such, and I can't figure out how to simplify it to just update a form field. Context:

• I have a Data form that has my events -- each event has a title and a number of available tickets
• I have a separate Registration form that uses Lookup fields to populate a dropdown with those events. There is a repeater that collects info on each attendee being registered.
• I have additional fields to total the number of repeaters, and then subtract that number from the available tickets--resulting in hidden fields that shows the Updated Total.
• I would like to update the Number of available tickets on the Data form with this Updated Total.
• (Presumably the next time someone loads the registration form, it will show them a new, reduced number of available tickets and the cycle can continue until the availability reaches 0)

Hope this is helpful