Decrypting files using the master key?

Hello there,

First of all, I have seen a few posts with the same question but their anwers are not the answers for my problem.

An user of my Nextcloud 11.0.1 instance has lost their password.
We tried resetting it using the administrator account while the recovery key was filled in but it didn’t change the private key of that user.

I’m not able to access it’s files.

Could you please help me?