You can use the same lockbox code to open the re-open the lockbox, get the keys again, and lock the car.
You can use the same lockbox code you just used or generate a new one through the app or website. Lock the car, then put the keys back in the lockbox and shut the lockbox firmly.
Make sure the car is locked, the keys back in the lockbox, and the lockbox securely shut before you leave. Fees apply for leaving the car or lockbox unlocked.