You have 2 options
As long as it isn't in a flext section of the board like the middle
Apply pva glue to the affected area
Then dip your balls in the wet glue and allow to dry
I think jezza is right about it breaking again if you fix it. If it has been caused by the stresses of normal riding and not an impact, it will most probably return when you start riding it again.
Pics would help us see how bad it actually is. I reckon your two choices are to continue riding it and keep an eye on the crack to make sure it doesn't get worse, or take it back to where you got it and see what the go with warranty is