I think this has to do with another question and I already answered reset on date question.
As far as a button to do the reset, you would need to create an admin page with a button on it. This button would have a JavaScript action attached to it. This JavaScript would run an AJAX request that would do the same thing as described for the other question https://support.advancedcustomfields.com/forums/topic/reset-custom-field-at-target-date/
