Some of the smallest PSR keyboards (E3xx series, I think) had the ability to store 9 registrations using the keypad. It had no dedicated registration memory buttons. Maybe that is what is meant here?
I think it's possible to save everything stored in the keyboard as a BUP backup file, but it's ages since I had to use a PSR-E3xx. All my students had at least an E4xx model before taking exams as even Grade 1 calls for fast registration changes, so my use of the small ones is very limited. (By Grade 2, most had upgraded to a pre-owned S9xx model!)
Assuming that you do have such a keyboard, now you have the settings safely restored, it would be worth reading through the manual about backups. If you find yourself needing more registrations as your playing requires them, perhaps consider an upgrade at some point - you'll never look back!