After you develop your down to a certain level, Lars will request materials to complete the repair on your motorcycle.

Reach Town Development Level 7 or Higher

Before you can get your motorcycle repaired, you have to develop the town to level 7 or higher. This will happen after you upgrade the benches in town, then turn in the next set of requested materials.

Hear Lars's Request

If you meet the above requirement, there will be a cutscene when you leave your tent/house in the morning. Lars will post requests for materials in the Olive Town Hall. You have to provide all three materials, not just one material.

Get the Requested Materials

Lars requests 1x Fulgurite, 1x Arthurite, 1x Olive Crystal. These can be obtained by using the bucket to drain ponds in the first, second, and third farm areas, respectively.

Give Lars the Materials

When you have the above materials, go to Olive Town Hall and check on the requests board to turn in all three.

The next day, there will be a cutscene when you go outside. After that, your bike will be parked next to your tent/house and you can use it as a mount.

How to Change Your Motorcycle's Color

After you receive the repaired motorcycle, you can talk to Clemens at Worker's Base Tool Shop to change the motorcycle's color.