Plug your CircuitPython board, via USB, to your iDevice using the appropriate cable.
On your iDevice, open the Files app, and tap on the drive labelled CIRCUITPY. Locate the code.py file within. Tap and hold on code.py and choose Copy from the menu.
Next in the Files app, navigate back and tap On My iPhone/On My iPad.
Tap and hold on an empty area, and choose Paste from the menu.
Open the App Store and search for the free app named Koder Code Editor and download/install it.
Open Koder and tap the new file icon in the lower left hand corner, tap Open Other App’s Files, then open the internal copy of code.py stored in On My iPhone/On My iPad.
Make changes to your code, then close the file – it will be saved automatically.
Return to the Files app and navigate to On My iPhone/On My iPad. Tap and hold on the edited code,py file, and choose Copy from the menu.
Navigate to the CIRCUITPY drive, tap and hold in a blank area, choose Paste from the menu, and then choose Replace from the popup that appears.