I have got two users on my iPhone app, one is based on my web account the others are local decks I guess.
How do I merge these decks in one account without deleting anything?
Second set of questions: How do I convert excel lists into anki decks? And how do I add these excel lists to existing decks?
Third set of questions: How do I learn vocabs in both directions? And is there a quick way to switch front and back if there’s a mistake in the deck?
For the third question, you can select one or more cards in the Browse screen, then use the Change Notetype action. You can assign the notes to the Basic (and reversed) notetype, or change the order of the fields.
The other actions need to be done using the computer version of Anki at the moment I’m afraid. You’ll need to export individual decks, then import them into the other profile: Synchronizing multiple profiles - Frequently Asked Questions
Anki can not import Excel directly, but it can read text files: Importing - Anki Manual