If second gear is stripped then as nocrf50 said its better to look for a new motor unless u are willing to to tear down the motor and split the casing. This then involes finding the problem then sourcing the part u need then putting it all back together including new gaskets so for what its worth the new motor is the better and easier option
i have riden a bike with that problem, a pitboss empire 125.
2 gear was wrecked.
either order a new gear box from someone off ebay, or buy a new motor for like 200 bucks.
option 2) put up with it