Official HP support pages typically only host the latest firmware. You may need to source older versions like FDP1CN1416AR from reputable third-party sites or community forums like Verify Model : Ensure the firmware is specifically for the (it often shares files with the 8610 or 8630). Step 3: Perform the Downgrade HP Printer Firmware Downgrade Guide - CompAndSave
Why downgrade?
The remains one of the most reliable all-in-one printers ever made – when it’s running the right firmware. The new downgrade method detailed above gives you back control over your device and your printing costs. hp officejet pro 8620 firmware downgrade new