First, you shouldn’t be leaving a job early without the customer’s explicit approval. They booked your services for a set time period and expect you to stay for that entire period.
That said, if you’ve completed the service to their satisfaction and they give explicit approval that you can go, they can request an hours adjustment by contacting the customer experience team. Note that all bookings carry a three hour minimum duration.
If you need extra time to complete the job to your level of satisfaction, you need to confirm with the customer that you need more time. Only they are able to add time to a job, so if you don't confirm it with them, you won't be eligible for additional pay.