Try going to HR but honestly I don't think you should get your hopes up.
There's been posts' about this before with multiple users in your same situation and the same outcome happened to every one of them.
They failed a drug test, they were recommended to take a drug prevention course which they had to pay for out of pocket, after completing the course the person they met up with will send MTA an email with your application in hopes of them reversing their decision, you'll wait a while, then you'll get a letter from MTA stating they've reviewed your case and they've determined that you're not eligible for the job and will not be hired.
On top of that you'll also be informed that you're not allowed to apply for any transit positions for the next year. I think the wait-a-year thing is a bit harsh but unless they've made an update to their 2018/2019 hiring process that I'm unaware of then it's still normal protocol.