The transmission mount is held to the skidplate by the four nuts that are recessed in the middle of the skidplate. You get to them from the bottom while laying on your back. Use a 1/2" wrench to loosen the nuts 3-4 turns and then insert the tcase spacer kit. Once the spacer kit is fully installed, simply retighten the four nuts.
The below photo indicates their position. The nuts you need to loosen are inside where the circle is. Skidplates vary slightly by model year and whether it is Mopar or aftermarket so yours will at least look close to this.