Solution No. 1 : When All of your RDS Roles Installed on one Server or Quick Deployment.
You can clone your current RDSH 1 server where applications installed. Add this cloned server RDSH 2 or whatever you named it , on your current RDS Farm Infrastructure, because it is clone server of your RDSH 1, you need to remove other RDS server roles on RDSH 2 server / cloned server.
In case of quick Deployment method you need to remove RDBroker, RDGateway, RDweb & RDLicensing on it. Rename the cloned server with static IP joined with you existing domain.
only applications is now available on it which is pre installed because its a clone of RDSH 1 Server.
Add this server on your RDS Farm Infrastructure, no need to create session collection on it, just add your new server RDSH 2 on your existing RDS Server and good to go.
RDBroker managed the session and an internal Load Balancing provided by RD Broker you can also set the weight according to the server load.
Solution No. 2
Deploye new server with installation of all of your existing apps which is on your RDSH 1 server, set as it is and add this server into your RDS Server.. now an internal algorithm provided by the RD Broker can manage the session collection with 2 RDSH servers, no need to create new session collection on newly added RDSH 2 server if you want to run same apps on multiple RDSession host.
Thanks
Asad