I took the index in the words, transformed the amount to binary, extra three zeros, calculated the sha256 digest, took the primary Section of the hexadecimal to transform it to binary, included 3 zeros on the 8 digits of your binary and received 00000010011 which translates to 19 in decimal. https://bookmark-group.com/story5225901/the-basic-principles-of-bip39-passphrase-generator