For words that have only 3 letters, there is absolutely no 4th letter. By way of example with the word “add”, there won't be any much more letters Later on and therefore should be the word "insert". The word “addict” is inside the BIP39 wordlist however , you would've utilised https://bookmarkmargin.com/story18871551/new-step-by-step-map-for-ledger-seed-phrase-bip39