1. Use transparent glue with good viscosity to stick and tear off repeatedly to remove some of the surface.

2. Use the 4b eraser used for drawing, which is very soft and can be erased.

3. If the marks that have been left for a long time have hardened, you can use a hot towel to soften them before trying again.

This should be able to be removed.

4. There is a solution for cleaning stickers on the market now; if you saw it on the advertisement on the car, you can ask around locally and it should be available.