Oh, that's similar to the XTM mammoth setup. It's a pawl design. You should see a hole somewhere in the sleeve for your center 2 speed assembly. Inside that hole, if you hold the gear but turn the axle, you should see at least 1 screw, but maybe two. One of those screws will be your two speed adjustment. Screwing the screw in will make it shift later. Backing it out will make it shift earlier. 1/4 turn adjustments are recommended.
The site doesn't show any good photo's of anything, so it's though to really point you at exactly what you need to do, but looking at the
two speed "transmission set" photo (which is horrible quality), it appears to be very similar to the XTM mammoth/XLB setup, just smaller.
Ok... XTM doesn't appear to make the mammoth anymore... but their MonsterMT has a similar more beefy setup. You can see the instructions on page 19 of the
Manual. What your adjusting is similar to part # 149666 on page 33 of the same manual. One screw holds the part on the shaft while the other screw adjusts the spring tension which controls 2nd gear engagement.
Now, I'm not saying this is identical to yours or anything, but it appears very similar in construction. Hopefully, reading the instructions on that manual will give you an idea how yours works and how to adjust it.