The left side main bearing is the "thrust" bearing on a blaster. It's nearly a press fit onto the crankshaft.
There is a tool used called a case splitter that screws into the two M8 holes inside the stator side and a large threaded rod pushes the end of the crankshaft until it slides out of the bearing (or the bearing comes out of the case, whichever)
You can buy the Tusk brand for ~$50 on Rockymountainatv.com or you can make one yourself by buying a automobile harmonic balancer puller and buying some extra long M8x1.25 bolts to engage the case. The harmonic balancer puller will save you some cash but it can't be used on 95% of ATV/dirtbike cases like the case splitter can.
No matter which direction you go, however, you'll need the crank puller to reinstall the crankshaft into the case. It's the opposite of the case splitter, it screws onto the crankshaft (using adapters) and then a long threaded rod pulls the crank back into the bearing. You COULD make one yourself but after you figured up fab time, the TUSK brand crank puller (at ~$50 on rockymountainatv.com) is a real bargain.
