Send data to specific client from another client with a server in middle[C#][TCP][UDP]

I have rented a windows server for my windows application which uses TCP and UDP for data transfer among many computers. I can do this locally by listening on the data requesting computer(Server) and connecting the data sending computer to it(Client). So I later found out that I must need a server which would have a public IP address(Just port forwarding won't work for every user). So I rented a windows server and setup my code listening to new clients on that server but how do I connect clients with each other for individual communication with each other?

The address format is server IP:server port. How can I listen, share and receive on same port? If not then what is the solution I can use?