ESP32 BLE client send "service UUID" to server

Hi, I've been trying to send the unique signature of a client back to an ESP32 server through BLE. The server is then supposed to send messages to just that one client alone using its unique signature. I'm not sure if this is at all possible and been trying using multi-connect servers and UART server, but can't seem to be able to do so. Can anyone help me, it will be greatly appreciated.