Don't do this! This advice is for Ledger Live, not the Ledger hardware wallet itself. If you reset your hardware wallet, you will absolutely lose access to all your accounts and crypto assets unless you have the necessary seed phrase +/- passphrase.
They still have their 24 words but the real wallet copntaing the bitcoin was also behind a pin number and a password , I think.
The 24 word seed phrase is necessary to recover both the dummy wallet and the hidden wallet. The hidden wallet also requires an additional passphrase which he set when he first set up the wallet. Without this passphrase, you cannot recover access to the coins in the hidden wallet.
Does your friend still have his original Ledger device in working order? If he does, and he remembers ever using a secondary PIN, then he can recover access to his hidden wallet using this secondary PIN without knowing the passphrase. He should then move all the coins out to a new wallet where he has properly backed up the relevant recovery data.
If he has not used a secondary PIN, or does not have access to his original device, then the only option to recover the coins is with the additional passphrase. If he does not remember this, then he will need to attempt to brute force it, but if it is at all long or complex then this will be next to impossible.