You´ll have to try one of the Trigger menus, the one that say´s Note 1st. If you put the cursor in the "1st" and move the dial, you´ll reach the Rim of the Pad, and change the sound.
If the problem is assigning the voice to the rim you can do this by switching selecting the pad with the touch. If you cannot do this you´ll have to change in the Utilities menu the Mode, I´m not in my home now but I think that menu has something to do with advanced edit settings that you have to turn to easy.
Maybe that´s not the problem, so you´ll have to try at one of the last Trigger menus, where you can select if your Rim is activated single, or with the pad.
If nothing of this works maybe it´s because your pad Isn´t stereo at all, and you should check if in the end of the pad theres an "s" wroted. If don´t nothing of the above will work.
I hope I´could help you, and I know It´ll sound like a punish but read all the manual, I don´t remenber all of course but I know somethings are in there, when I get in to trouble.