Decrypt recovered *.pst from encrypted disk

I accidentally deleted an Outlook “.pst” file and used PhotoRec to undelete the file. The file was on a encrypted disk. The file was recovered with the exact same size, however the filename and extension has changed. The file was initially called “hm.pst” and now is called “f599212.gpg”. I have tried to use Gpg4win to decrypt the file, however no key is available on the keyring, I have tried this using the computer where the file was stored. I have the password but i don’t know where can i find the key.

Can you help please?

Thanks in advance.