I lived in NY 5 yrs ago, but for some reason my employer deducted $400 this year and I don't know what form to fill out, or how to get that money back. Thanks in advance

If you did not live or work in NY, you do not pay NY tax. Now file NY return and claim the credit. Attach statement from employer that you do not live or work in NY.

Or talk to your employer. See if they can take care of this situation as they have not yet filed final state tax return for employee taxes.