Marilyn, What Model-Year Is This Highlander ? I Don't Know How Many Technical Service Bulletins I've Seen From Different Manufacturers That Say It's Normal.
Give the model-year and I'll try and check.
I wouldn't drill into it. You can try temporarily removing the moisture by removing the bulbs and ltting th sun dry the capsule or use a hair drier on the lens, but be careful not to get it so hot that it melts the plastic.
A permanent fix is probably a new headlight capsule. Oldschool has outlined GM's approach to this issue while a vehicle is under warranty. Depending on the model-year, sometimes a salvage yard unit makes sense and you can look for one with no evidence of condensation.
Do you need the lens to be totally clear to pass an inspection where you live ? We have no inspections of any kind where I live and I'd try one of the above suggestions when it bothered me enough.