"What is the best, if any at all, way to removed the dots or minimize them?"

Apply another coat of finish more uniformly.

[Sigh]
> my hardware store salesperson told me to spray polyurethane.

Probably not the most brilliant idea.

Not seeing it, I'd probably recommend scraping off the spots. If you don't have a finely tuned cabinet scraper, get some utility knife blades, dull the corners and hold them between your thumbs and index fingers. Tilt the blade about 10 degrees from vertical away from you and push lightly with your thumbs. You might need to adjust the angle a bit forward or backward to get a good cut.

Then using a sanding block and 400 grit sandpaper, lightly dull the whole surface. Wipe off the sanding dust with a cloth dampened in mineral spirits. Wipe on another THIN coat of polyurethane, either a canned "wipe on poly" or regular poly thinned 50-50 with mineral spirits. Use a lint-free cloth or a blue shop towel. Did I say THIN coat?

A better choice would have been to apply lacquer, as that's almost certainly what's on there now. It will bond to itself creating "one coat" of finish. But since you've applied the spray poly already, it's too late for that as the lacquer will be too "hot" for the poly and can blister it up.