To unlock The Art of Bike Repair trophy in Days Gone, you will need to apply 100 scrap to your bike.
Scrap is used to repair your bike, which will become damaged by crashing, driving through water or performing jumps.
You will collect scrap in many locations throughout the game, although the quickest way to collect it is car motors. Once you use 100 scrap to repair your bike, the trophy will unlock.
You can track your progress towards the trophy in Storylines > Trophies > The Art of Bike Repair.