Adding INSERT key to iTerm2 on macOS

Go to iTerm2 preferences ⌘ + ,. Click on Keys and add a new keyboard shortcut (plus button near load preset button). Press your desired keyboard shortcut (for example option + F12) after that change Action to Send Escape Sequence and fill Esc+ with [2~. After that, you can emulate the insert key with your keyboard shortcut.

Or if you just need insert key in Midnight Commander use ctrl + T