Here is a video tutorial.
2. Inspect your old mouthpiece: check for holes or tears, check if bite tabs are intact
3. Carefully cut off the old mouthpiece with wire cutters
4.Check if the new mouthpiece has an orientation: Is the top indicated or is there a brand on the top?
5. Put the new mouthpiece on the 2nd stage
6. Get your matching zip tie and make sure that it is oriented downward and that the lock is on the right or hose side of the mouthpiece
7. Tighten it down with the zip tie tool or pliers if you don't have one
8. Cut the excess zip tie off so that it is flush with the lock