HP Officejet Pro X551 Printer series - Manual (Page 165)

3. If the jam cannot be cleared at the tray, try
clearing the jam from the Tray 3 left door.
4. Close Tray 3.
NOTE: To close the tray, push in the middle
or with even pressure on both sides. Avoid
pushing on one side only.
Clear jams in the left door
1. Open the left door.
ENWW Clear jams 151