Find a tiny drill bit, drill a hole in the area it goes down, about 1 inch away from the seam. Get a tube of paintable caulk and cut the tip to just over the size of the hole you drilled. Carefully begin to push caulk through the hole until you feel it start to push the seam upward. Stop, then place a heavy object over the area so it presses the plank flat with the surrounding area, a 12-inch square board with a huge bottle of laundry detergent would work well.

Allow to dry for 2 days, may be more.

When dry the caulk will still give a little, but not as much and should deaden the click.

Any exposed caulk can be shaved down carefully with a razor. Get a sharpie that matches your floor color, darker is better than lighter, and color the paintable caulk hole.

If that doesn't work you need to remove the bad piece of lvp and replace it.