Could you help me do it if it's possible?
Maybe I can... but no promises.
I wrote
btcrecover exactly for this purpose, but I've found that the biggest challenge to password recovery sometimes isn't technical, but instead it's the language difference.
There's a
Tutorial here, but it's in English which I'm sure will make it difficult to understand (and I don't speak French, sorry).
If you can provide more specific details on the password you're trying to find (PM me if the password details shouldn't be public), I'll try to help out (but it would still be up to you to download btcrecover and run it on your own computer)....