Что то подобное я делал
сначала надо выделить окно
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowsName As String) As Long
Private Declare Function SetForegroundWindow Lib "user32" (ByVal hwnd As Long) As Long
Private Declare Function ShowWindow Lib "user32" (ByVal hwnd As Long, ByVal cCmdShow As Long) As Long
Private Sub Command1_Click()
Dim lFoundWindow As Long
Dim lOK As Long
Dim lOK1 As Long
Dim X As Variant
lFoundWindow = FindWindow(vbNullString, Text1.Text)
If lFoundWindow = 0 Then
MsgBox ("такого нет окна")
Else
lOK = SetForegroundWindow(lFoundWindow)
lOK1 = ShowWindow(lFoundWindow, 9)
lOK1 = ShowWindow(lFoundWindow, 10)
lFoundWindow = 0
lOK = 0
lOK1 = 0
End If
End Sub
потом найти хэндл окна(кнопки которую нажимать надо) с помощью
EnumChildWindows и FindWindow
после чего слать сообщение на этот хэндл
типа вот какой то кусок кода разберешься
---------------------------------------------------
Option Explicit
Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As Any, ByVal lpWindowName As Any) As Long


Public Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" _
(ByVal hWndParent As Long, _
ByVal hWndChildAfter As Long, _
ByVal lpClassName As String, _
ByVal lpWindowName As String) As Long


Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
(ByVal hwnd As Long, ByVal Msg As Long, wParam As Any, lParam As Any) As Long

Public Const WM_LBUTTONDOWN = &HF5 'с этой работает нажатие!!!!!!! 245*&HF5
'Public Const WM_LBUTTONDOWN = &HD
'поиск хэндла кнопки
Public Function find_hwnd_button(klass As String, name_button As String) As Long
find_hwnd_button = FindWindowEx(FindWindow(vbNullString, "кнопка_"), ByVal 0&, klass, name_button) 'определяем дескриптор кнопки
MsgBox Str(find_hwnd_button)
'***************************************************
'hBut = FindWindowEx(FindWindow(vbNullString, "кнопка_"), ByVal 0&, "ThunderRT6CommandButton", "старт") 'определяем дескриптор кнопки
'класс окна ("ThunderRT6CommandButton") определяем прогой типа spy!!!!!!!
End Function

'посылаем нажатие кнопке
Public Sub send_сlick_button(hBut As Long)
Call SendMessage(hBut, WM_LBUTTONDOWN, 1, 1)
End Sub