Travel to the West Tek research center and enter via the back, as the super mutant that must be killed is usually in the acid pool room. One will encounter some high level super mutants and mutant hounds. Once the skirmisher is killed, return to the settler forager for a reward.
Talk to Settler Forager
I agreed to help him protect Appalachia by killing the Super Mutant Skirmisher
Travel to West Tek Research Centre and kill the Super Mutant Skirmisher