Auto populate Account information on Service Request based on Site selected

Summary:

Users only have information for the site where the service request needs to raised. Need to populate the Account related to the site automatically.

Content (please ensure you mask any confidential information):

Can we know if this is possible and should we use Groovy and at which event should it fire.

Version (include the version you are using, if applicable):

25A

Code Snippet (add any code snippets that support your topic, if applicable):