Please don't take offense at this, because I certainly don't mean it that way, but living in Singapore, have you ever had mashed potatoes before? Because the basic recipe is really supposed to be somewhat bland. If you add too much salt, all you'll end up with is salty bland mashed potatoes - lol!!
I'd suggest you do one of two things: 1) add more salt & pepper to your individual servings of mashed potatoes - NOT to the entire pot, &/or 2) add other ingredients to "spice things up" - add garlic, cheese, buttermilk, sour cream, bacon bits, chopped cooked greens, gravy or any other sauce you're fond of, etc., etc. Experiment - that's what makes cooking so much fun. Unless you're working with really really expensive ingredients, the worst that can happen is that you don't like the current result & can easily try again.