Sending mouse clicks to other applications

If your next question is how to get the hWnd of a Window, use the FindWindowEx API.

Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long
Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long
Private Const WM_LBUTTONDOWN = &H201
Private Const WM_LBUTTONUP = &H202
Private Const MK_LBUTTON = &H1

Private Sub Command1_Click()
    
    Dim HwndOfWindow As Long
    HwndOfWindow = FindWindowEx(0, 0, "SciCalc", "Calculator")
    
    If HwndOfWindow <> 0 Then
        'Click it
        PostMessage HwndOfWindow, WM_LBUTTONDOWN, MK_LBUTTON, 0
        PostMessage HwndOfWindow, WM_LBUTTONUP, MK_LBUTTON, 0
    End If
    
End Sub