myFinalCode:

Public Function func_1() As Double
'MS Access module

    Dim xlapp As New Excel.Application
    Dim wkb As Excel.Workbook
    Dim wks As Excel.Worksheet
    Dim arg1 As Double
    
    Set xlapp = CreateObject("Excel.Application")
    xlapp.Visible = True
    Set wkb =  xlapp.Workbooks.Open("C:\Book1.xlsm")
    arg1 = 100
    xlapp.Run "func_2", arg1

    'Thank you all very much!    

End Function