Download and install the driver and software from here: https://epson.com/Support/Scanners/Perfection-Series/Epson-Perfection-V500-Photo/s/SPT_B11B189011
Make sure the reflective mat is removed from the top lid (slide out toward front of scanner). Now you should see glass on the lid as well as the scanner base.
Carefully remove all visible dust from the glass with a microfiber cloth. If there are smudges or marks on the glass, use regular window cleaner, and be sure to dry it 100%
Make sure the negatives are as clean as possible, but be extremely careful not to scratch them or get figerprints on them. I use a clean microfiber cloth to remove large dust particles and hair. You can use puffed air, or soft antistatic brushes as well.