There are several ways to allow a user to book a specific vehicle when required.
Dedicate a vehicle to a user or a list of users
You can dedicate a vehicle to a selected user or a list of selected users following the steps in this article.
Add driver to Dedicated/Private vehicles
A dedicated vehicle can only be booked by the dedicated users and not others.
Setup a user with a preferred vehicle
You can setup a preferred vehicle for user, by going to the user's profile, and then select the registration in the Preferred Vehicle field.
When making a new booking, the vehicle availability will default to 'Preferred', and the selected vehicle will be assign to this user as long as it is available.
Using vehicle accessories
You can setup a vehicle with accessories, then user can book that vehicle by specifying the required accessory on the new booking page or multi booking page.
To create a new accessory, go to Maintain Vehicles - Vehicle Accessory, click on Add New Record, and enter the Code and Description of the accessory then hit Update.
Once the accessory is create, you can assign it to a vehicle by going to Maintain Vehicles, find the vehicle then click on Edit, select the record from the Accessories dropdown list located at the bottom of the page, then click Update Details.
When making a booking, a user can select the appropriate accessory on New booking page or Multi Booking page to get an appropriate vehicle.