Find what servers are using a specific RDS Licensing server ?

Let's say that an existing environment have RDSL1 and RDSL2. The majority of servers in the domain are using one of both as their RDS Licensing servers, 

We plan to consolidate our 2 RDS Licensing servers in a new RDSL3, we need first to push all servers that are using RDSL1 to start using RDSL3,

My question: How to find the servers which are using RDSL1 only ?

Thank you,

Moad.