If you are using AirPrint to directly to the HP from the iPad, rather than printing via a shared queue on a Mac, then you will need to change the name registered in the printer.
If you know the IP address used by the printer then you can connect to its internal web page by typing that IP address into a web browser. Once there you will see some menus that should let you change the name.
If you don't know the IP address then you can open Safari on the Mac and select to show all Bookmarks. Then from the sidebar, select the Bonjour entry. This should show the HPs on your network and selecting either will also take you to their internal web page.
Or, there should also be a way that you can change the name used via the touch panel on the printer.