Choose Your Fighter sends you to Provis Strata at 12 o'clock in the center of the map because your objective will be to kill Mawsworn. When you reach the quest area, [npc=180927] says to pick a fighter. Step away so you can check out tooltips without picking the fighter nearest you. This isn't a vehicle quest, you are picking a Guardian. There are three humanoid automa in a row:
- [npc=181728], a healer in brown armor
- [npc=181729], a tank in light blue armor
- [npc=181727], a DPS in dark blue armor
If you've picked wrong, just make the best of it and kill nearby Mawsworn - which you probably did before without a Guardian. I abandoned the quest, and had to return to Pilgrim's Rest to pick up the quest again from [npc=181179]. Then I had to run back through trash to pick up a fighter. (With flying getting there and leaving is less hazardous.)
Check the mini-map for the treasure symbol, since a [object=375272] sometimes spawns in the area and the fighter may be useful in dealing with trash.
When you're done, your fighter will escort you as far as the circle road.