getting Index of "PlayerController" Not for a Game

Hey there,
Iam sending data from multiple player controllers to a server (gamemode). Now i want to do this: Each player controller joins on a dedicated server and sends data via replicated events to the server. The server should now know which playercontroller send which data. I need this, because the playercontroller (a program on a computer in lan network) should send a string for example to the server. So all player controllers in the network should send strings, which are modified by the server depending on which index the sending playercontroller has.

If anyone has ideas, i would be so happy