Why not try to tell him to connect his ledger to Electrum and follow Lucius's suggestion above.
Or get the master public key of that wallet and use a tool called xPub analyzer you can find it here https://blockpath.com/wallets/new?action=appxpub
It could scan all possible paths and find the used addresses.

Another option is the tool from Ledger they have their own xPub scanner created a few months ago and this should be the tool you must use if you want to recover your wallet.
Here's the link:
- https://blockpath.com/wallets/new?action=appxpub