1) Decrypt the save on your 9.00 first (with PS4 Save Mounter 1.9.3 version by ctn123).
2) Grab the mounted decrypted files to PC. (Nice to keep backups)
3) Then put them on your 5.05 with Save Mounter 1.5 (5.05 only version) ( that's if you can't get 1.9.3=universal fw) to work on 5.05.
Importantly the game update that save was saved on, usually needs to match what was used by the save originally.
So if it was saved on v1.12 you can't use on v1.00 game, you can install it, but it will say update game version to use save.
Decrypted saves - can work any firmware.
Encrypted saves - Will need the firmware the saves were saved on to decrypt.
You can also decrypt lower than your current firmware.
And saves encrypted from system software higher than your current firmware - you can't decrypt.
If it's from latest firmware then you'd need to pay for Save Wizard to decrypt it.