I took the index with the words, transformed the selection to binary, included a few zeros, calculated the sha256 digest, took the initial part of the hexadecimal to convert it to binary, included 3 zeros for the 8 digits of the binary and got 00000010011 which translates to 19 in https://hylistings.com/story20086999/the-5-second-trick-for-ledger-seed-phrase-bip39