VBA Excel: Get the clicked cell´s adress on another workbook

I have an excel file A with a macro and I have to retrive a cell´s adress in another excel file B by the user´s click on it.

The macro looks like this.

In the Class:

Public WithEvents appevent As Application

Private Sub appevent_SheetBeforeDoubleClick(ByVal Sh As Object, ByVal Target As Range, Cancel As Boolean)
ClickedCell = ActiveCell.Address
End Sub

In the Module

Sub ClickedCellSub()
Dim WbA As Variant, WbB As Variant
WbA = ThisWorkbook.Name
WbB = "B.xlsx"
MsgBox "Please double click on the Assembly SS 00 you want to compare"
Set myobject.appevent = Application
Workbooks(WbB).Sheets(1).Activate
Set myobject.appevent = Nothing
MsgBox ClickedCell
Workbooks(WbA).Activate
End Sub

The problem is, the macro doesn´t wait for the event DoubleClick on the other excel sheet and goes to the end.

How can I stop the macro until the event happens?

Many thanks in advance!