To access the reset line on the XStick, you first need to separate the plastic housing. The XStick's housing is held together by four posts, one on each corner. A wide tipped flathead screwdriver should be able to separate the two halves without damaging the plastic.
The following illustrations show where the reset and ground pads are for the two types of XStick. To perform a reset, bridge the reset pad to the ground pad using a peice of wire. The XStick must be plugged into a USB port and powered on for XCTU to detect the reset.