Not too difficult.
Connector tab. Select D-STAR/REF/XRF (DPlus/DExtra)
Modem setup as required for your radio.
Server: <repeater callsign>
Module: <choose from what RF bands the repeater has, one of A or B or C>
Callsign: <your callsign>
If you enable Advanced mode you should be able to set your local module too, I use <space> which is entered using the space bar, make sure you have only 1 character entered.
Click save, it should connect but look for status and log information on the Status tab with Advanced mode enabled.
Not sure I can help you much more, it will rely on the repeater being correctly configured and if like my local one it's inside a VM with the Icom G3 program and other things on the repeater site it might not work if the port forwarding on the router at the repeater end is not correct and forwarding to the VM or repeater.