Make sure weapon is unloaded!
Push takedown and pivot pins out and remove lower from upper receiver. Remove buffer and spring from lower by pushing the buffer retainer down and pulling them out of the buffer tube (as shown on page 25 in your owner’s manual).
Put lower receiver in a magazine well vise block and loosen castle nut with a properly fitting telestock wrench. Twist buffer tube clockwise slightly and remove takedown pin spring.
Hold buffer retainer down and unscrew buffer tube. Slowly release the buffer retainer and leave it in its hole in the receiver. If you don’t hold the retainer when unscrewing the tube the buffer retainer and spring will shoot out of the hole and can become lost.
Unscrew the buffer tube all the way out of the lower receiver and remove the stock endplate. Slide the tactical endplate on in its place with the raised area up as shown.
Screw buffer tube back into the receiver. Hold buffer retainer down and screw the tube in all the way until it stops against the retainer post, then back it off one turn. Insert takedown pin spring back into the hole in the back of the receiver.
Turn stock so it is straight and press the endplate up against the receiver compressing the spring straight back into the hole. Screw castle nut up against the endplate.
Re-tighten castle nut and replace buffer and spring.