Create resolver for field which lives in another graph

[rnoack1]

I'm not sure this is an issue with code, or documentation or my understanding. Hope this is a valid place to ask and someone could give some input.

I have a federated graph, where base type is defined in one subgraph, and that type is extended in another graph.

I can not figure out how to represent this, using the "resolveReference" provided by this package:

For example:
https://www.apollographql.com/docs/federation/entities/#resolving

In the example above, say that one graph provides "Product" , and now I want to add field "Reviews" on to product. How would I represent this using the transformSchemaFederation function? Since it provides only "resolveReference" , but does it provide the ability to provide resolvers for specific fields?