HP LaserJet Pro 400 color Printer M451 series - Manual (Page 177)

2. If necessary, push the guide (callout 1) and
remove any visible paper (callout 2) from the
bottom of the delivery area.
NOTE: If the sheet tears, make sure that all
fragments are removed before you resume
printing. Do not use sharp objects to remove
fragments.
3. Close the rear door.
ENWW Clear jams 159