Canon DR-2580C Service Manual page 216

2
Set the Document Guide Adapters onto the Document Guides.
Note
Cover the Document Guides from above with the Document Guide Adapters,
and insert them as far as they will go, until they click into place.
3
Carefully close the Upper Unit.
IMPORTANT
Do not force the Upper Unit to close. Doing so can damage the scanner.
4
Be sure that the Upper Unit is completely closed by pushing on both edges
with both hands until you hear a click.
46
Using the Scanner