Not quite sure what your setup is but the fact that a(ny) control is placed on the form itself on on a tab control which is itself placed on the form makes no difference in how you reference the control.
So if you want to requery a control on the main form (regardless if placed in the header, detail, footer or a tab control on any of those three sections) from a subform placed anywhere on the same form (including on a tab control) you could use
Code:
Me.Parent.Form.Controls("txtYourTextBoxToRequery")