Not able to auto select Action plan on creation of new service request

Summary:

We want to auto associate the Action plan "New Partner Request" when a Service request record is created in system.

When we try to write a groovy code for the same we do not find any relation between Action Plan and service Request objects which can be used to do setAttribute on one of the attributes of service request.(to set the action plan in it automatically)

When we try the same approach via REST API, postman and try to send patch a body to Service request, it only attached the action plan with service request and we are not able to see the actions inside that action plan because the Action plan " New Partner Request" has