Hi,
You have to write JavaScript that will fire on change of license Plate. The JavaScript will perform the below operation.
- Read the License Plate value.
- Retrieve License Plate and Account related information.
- Set the Account Retrieved from License Plate
- Set the Fields Retrieved from Account.
You can achieve this through Odata Or Soap JavaScript.
For OData refer below blog. Using Expand you can fetch both License plate and related account information in one Query.
https://community.dynamics.com/crm/b/mahenderpal/archive/2012/11/21/retrieve-primary-entity-and-related-entity-data-using-odata-in-ms-crm-2011.aspx#.UgzO1CS3QdU
For Soap refer below blog. Using LinkEntity you can fetch both License plate and related account information in one Query.
http://mileyja.blogspot.in/2011/03/crm-2011-retrievemultiple-calls-in.html
Hope this helps!
Thanks!