To complete one of the Bullseye challenges, you'll need to complete a glider run over Dusty Depot after jumping off the Battle Bus. To achieve this, nothing too complicated. All you have to do, once the bus is above the farm, is to jump and control your fall to pass through the rings.
For this challenge, you will therefore have to jump from the battle bus above Dusty Depot, and complete the aerial circuit by passing through 4 rings which constitute the path to follow. These four checkpoints cannot be avoided, and the challenge cannot be completed if the circuit is not completed after jumping off the bus only.