Trying to figure out how a mayor helped healthcare

Mike Bloomberg the former NYC mayor running for President's most recent ad saying he helped uninsured get insurance and all kinds of crap. Now i know a governor can help and a president can help but how the hell does a mayor do such. I think its just more I'm so great Trump's so bad ad. He even has a foreigner on there thats supposedly a nurse saying how he made the changes. Probably paid for liberal maybe even an illegal cause we know the leftist loves those.