For vba, you'll need to learn how to reference a subform on a form. If I recall, for a control, it's
[Forms]![Main form name]![subform control name].[Form]![control name on subform]
To requery a subform, you don't have to go as deep:
[Forms]![Main form name]![subform control name].[Form].Requery
NOTE - [subform control name] is NOT the subform name. It is the control on the main form that contains the subform. Nor should it have the same name as your subform.
You should be able to requery the sub form using your main form button click event with the syntax I posted.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.