Beware of the terminology!
I assume you want to assign a rig that you like to a preset in the FCB, let's say Bank 1, preset 1.
Normally on Bank 1, preset 1 the FCB sends a PC ( program change) No. 001, on bank 2 preset 2 no. 002 etc.
To assign a rig to PC no. 001 now go to the Kemper's rig menu and do it from there.
The FCB itself is very difficult to program on the device itself, therefore I recommend using the LG-FCB editor.
I also recommend updating the FCB Firmware with the UnO chip V. 1.03, as you get a lot more stompbox functionality in the FCB.
Info here: http://www.lg-fcb.com/lgfcb_software.php for the editor + http://www.ossandust.be for the UnO.