Code:
 Private Declare Function Add Lib "AComDll_Thread" (ByVal A As Long, ByVal B As Long) As Long

Private Sub Form_Load()
    Dim DllPath As String, NowPath As String
    DllPath = App.Path & "\dll"
    DllPath = "Z:\test"
    NowPath = App.Path
    ChDrive Left$(DllPath, 2)
    ChDir DllPath
    '-----------------------
     MsgBox Add(3, 4)
    '-----------------------
    ChDrive Left$(NowPath, 2)
    ChDir NowPath
    
    MsgBox App.Path
End Sub