Here is my code:
keybd_event(VK_MENU, 0, 0, 0);
keybd_event(VK_RETURN, 0, 0, 0);
Sleep(200);
keybd_event(VK_MENU, 0, KEYEVENTF_KEYUP, 0);
keybd_event(VK_RETURN, 0, KEYEVENTF_KEYUP, 0);
The first line would press Alt
The second line would press Enter ↵ (or Return ↵),
The fourth line would release Alt,
The fifth line would release Enter ↵ (or Return ↵).