Try Forms!MainFormNameHere.SubformControlNameHere.Form .Requery
or if the code is on the main form, can use
Me.SubformControlNameHere.Form.Requery
Other syntaxes may work but I find neither of those has ever failed to work, unless you have a navigation form. That is a different animal.
Your subform control name might be the same as the form you're using as the subform. I don't allow that.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.