For words that have only 3 letters, there is no 4th letter. One example is with the word “add”, there aren't any extra letters afterwards and so should be the word "increase". The word “addict” is inside the BIP39 wordlist however , you might have made use of “addi” for https://socialmediaentry.com/story4314204/the-5-second-trick-for-ledger-seed-phrase-bip39