Bip39 Checksum. You would then do a fundamental recovery by using a command similar to the a person below. (This command works by using a sample wallet file bunlded with BTCRecover) Anyone else who discovers the phrase can steal the bitcoins. It must be stored secret, by way of example https://bookmarkworm.com/story18979576/bip39-wallets-https-linktr-ee-bip39-getting-my-ian-coleman-bip39-to-work