I used to have a white laminate countertop and used Soft Scrub Gel to brighten it. They also make a polish for laminate.
There is some helpful information here:
Hi R Allen,
By dull do you mean the color or is it lacking the shine? If the color is dull, I'd try baking soda first. Sprinkle it on the counter, spread it with a sponge/rag and warm water. Let that sit for a while to give the baking soda time to work, then scrub and wipe it all off with warm water. If it's missing the shine, I've used car wax on my laminate countertops in the past. It will need to be redone occasionally, but it does help. Wishing you the best.
Try using Barkeepers friend. It might do the job for you.............
Here is a great post https://www.diynetwork.com/how-to/rooms-and-spaces/kitchen/how-to-paint-laminate-kitchen-countertops
Cleaning them and then waxing them really brightens them up. Avoid abrasives as they will dull the finish even more.