How do i decrypt single ECRYPTFS_FNEK_ENCRYPTED.F.....etc Files within the Linux Mint system?

I have a NAS RS816 - All my folders are encrypted, A user created a backup of a access file and then by accident deleted the file... I managed to recover the directory which contains 11 files. Each file has been named ECRYPTFS_FNEK_ENCRYPTED.F........etc I would like to decrypt each file using the password which was used to encrypt them, I also have the .key file How would i do this, I have tried the Sudo ecryptfs-recover-private but it does not file the files and when i try run the folder in terminal it still does not find the files Kind Regards