Private Sub Command0_Click()
        s = InputBox("What is the Mill ID?", "Mill ID", "")
        Me.RecordSource = "SELECT * FROM MyTableWithMillData WHERE Mill_ID = '" & s & "'"
End Sub

Private Sub Command0_Click()
        s = InputBox("What is the Mill ID?", "Mill ID", "")
        Me!subformcontrolname.Form.RecordSource = "SELECT * FROM MyTableWithMillData WHERE Mill_ID = '" & s & "'"
End Sub