If you still cannot find the appropriate settings then I suggest you contact HP and ask for thier assistance. They should be able to walk you through the process to configure your printer in the way that you want.
That being said...
Hidding a SSID is not an effective security technique. Many refer to hidding a SSID as "security through obscurity" technique which is really not security at all. This is especially true in the scenario that you identified where a malicious user has been targeting your printer for months at a time. All it takes is for someone to stumble across the Access Point when searching the airwaves and boom, there goes your "security". What really secures your wireless is the use of strong/high entropy passwords and the latest WPA2 wireless password protocol. That way even if someone happens to find your wireless they wont be able to get into it.
Test your password strength:
https://howsecureismypassword.net/
Turning off the wireless would be much more effective than trying to hide the SSID.