To refund a vehicle deposit go to Vehicles > Reporting > Accounts > Deposits. In this report you can use the filters to find the deposit you are looking to refund.
If you'd like to read more about the Vehicles Deposit report you can find that article here.
To refund a deposit double-click on the line in question and it will bring up this pop up;
When you select the Refund radio button it will open up the total field allowing you to amend the value of the refund you will be processing. You can amend this to any value as long as it is lower than the original deposit value.
If you do not refund the full amount you can come back and repeat these steps until the full deposit is refunded if necessary.
Add notes as required in the field at the bottom of the screen for a narrative on the refund and hit the next button. It will ask you to confirm you are sure and then a credit note is produced using the same payment method as the original.