puedes hacer una funcion para enviar teclas a esa ventana u ysarla como SendKeys
Hice esta funcion, no se si funciona pero pruebala
Private Declare Function SetActiveWindow Lib "user32" (ByVal hwnd As Long) As Long
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Public Function SendKeysEx(Ventana As String, Tecla As String, Optional Espera = 0) As Boolean
On Error GoTo error
Dim Ventanita As Long
Ventanita = FindWindow(vbNullString, Ventana)
SetActiveWindow Ventanita
SendKeys Tecla, Espera
SendKeysEx = True
Exit Function
error:
SendKeysEx = False
End Function
Llamala usando SendKeysEx("Nombredelaventana", "Tecla")
saludos