The user likely needs to install or update the HP driver:
Option 1: Launch App Store and select Updates. The drivers should appear under "Updates Available." Update the drivers.
Option 2: Go to https://support.apple.com/kb/DL907?locale=en_US, click Download, download and install the driver.
If there is no Pharos popup window after the install, restart the laptop.
If you restart and still don't get the window, try reinstalling Pharos. On a Mac...
First, run the uninstaller. Go > Computer/Macintosh HD/Library/Application Support/Pharos/Utilties/Uninstaller.
Reinstall Pharos.
Restart the laptop.
If you restart this second time and still don't get the window, confirm the Pharos Popup is installed and add it to the Login Items. On a Mac...
Go to System Preferences > Users & Groups (Lion, Mountain Lion) or Accounts (Leopard, Snow Leopard)
Click the Login Items button beside the Password button at the top of the window. Look for the "Popup (All Users)" item in the application list. If you do not see this item...
Click the + button below the application list.
Navigate to Macintosh HD > Library > Application Support > Pharos
In the Pharos folder select Popup
Click Add
You should now see the Popup (All Users) item in the application list. Restart the computer and try to print a document. If you do not get the Pharos Popup after restarting, they'll need to see someone in STS.