What should the customer service do if the owner complains that the parking space is occupied?

First of all, customer service should understand the situation clearly.

After receiving the owner's application, the customer service should contact the owner of the parking space in time and take the initiative to get in touch with the owner to let the other party drive into the parking space.

If you can't get in touch for the time being, communicate with the owner of the occupied parking space to ease the mood of the other party and think of some solutions later.