If you mean you wish to remove it DONT!
It is a vital safety devise & should be in working order.
If you just need to reset it.
Most chain brakes are operated by the front hand guard. The guard gets pushed forward if the saw kicks back up at you.
Pull the guard back towards the saw. It may need to go a little past where its usual position is. You will normaly hear a click when brake resets. Let guard spring back to its usual position and you should be in action again. If the brake does not release something may have jammed or broken & the brake will need repair.
I hope this has helped.
Robin S
September 2008