Dell B5465dnf Mono Laser Printer MFP - Manual (Page 233)

Cleaning the scanner glass
Clean the scanner glass if you encounter print quality problems, such as streaks on copied or scanned images.
1 Slightly dampen a soft, lint-free cloth or paper towel with water.
2 Open the scanner cover.
3 Remove the white underside of the scanner cover.
Maintaining the printer 233