I took the index in the words, converted the number to binary, included three zeros, calculated the sha256 digest, took the very first Element of the hexadecimal to convert it to binary, included 3 zeros to your eight digits on the binary and acquired 00000010011 which translates to 19 in https://socialfactories.com/story4254063/bip39-seed-phrase-mnemonics-generator-an-overview