(Regards this API api/src/main/java/com/ichi2/anki/api/AddContentApi.kt and Third Party Apps · ankidroid/Anki-Android Wiki · GitHub)
Right now, editing existing notes through the AnkiDroid API isn’t very practical. You can update notes if you have their noteId, but that means third-party apps have to keep track of all those IDs themselves - which is pretty inconvenient and easy to mess up.
It’d be a lot easier if the API let you search for notes based on field content (like the front of the card) to get the noteId when needed. Also, some way to delete notes through the API would be also good, but I guess this would be a bit sensitive.