The instructions should be fairly clear about this. You drill out the 4 existing holes per damper rod, and add another pair of holes on each rod. You're drilling them out to 5/16" (8mm). You should end up with 6 such holes per rod.
The center of each hole should be about 10mm away from another (spaced axially, lengthwise) and be perpendicular to the last set so as not to weaken the rod.
If you're uncomfortable doing this, or want the option of going back to stock, the Traxxion kit comes with their own damper rods, but costs like $80 more.