Sorry : playing myself with openLRSng and telemetry so the OPlink specifics I do not know.
On the GCS you can select in the drop down list which port to use for telemetry. As long as you have an USBCom dongle, you will have on the computer a serial port that can be directly wired to your quad serial ports. On the quad side, the UART should be defined as "telemetry" (i.e UAVTalk protocol). From then on you can adjust baud-rates and validate that everything works correctly.
Once this is working I usualy insert my telemetry modules in between and make sure these are using the same baudrates as the ones that were successfully tested. As said I am not using OP-Link so not exactly comparable but you get the idea.