is it an express, express 2 (NC50), urban express (NU50 - little funny chopper wannabe) or express SR (NX50 - tiny scooter with legshields)?
To me, bystarter is what they called the autochoke, which was only on the NU and NX. if you have an NC50 express, you probably don't have it and the manual is referring to the ones on the other expresses that did.
it's basically an autochoke that dumps some excess fuel for cold starts. But sometimes they fail anyways and folks just remove the hoses and plug them at the carb anyway. so even if you did have it you don't really need it, especially if you've got a functional choke on the carb or can choke it by hand.