Which service should contain code for many to many relationship?

Let's say that you have a Rack Table and a Bike table. Then you also have a RackBike table that links which bike belongs to which rack and maybe in what order. The structure of the tables is bike and rack tables have id and name column and RackBike has RackId, BikeId, and Order.

To my understanding, in a micro-service world, there is a service for Bike and a service for Rack. Lets call them IBikeService and IRackService.

My question:

Which service would contain the code for Adding/Modifying data to RackBike table? Would it be The Bike Service, the Rack Service or would it be a new service to handle the CRUD of that? And why?