Dual status tax return

I assume, I need to file a dual status tax return for 2016, because I work in the US from May. I've started to use your system, but I don't find any option for this situation. Where can I attach a 1040NR to my tax return, and how can I figure out the exact date when my non-resident status has changed? Can I find it on my W-2, or in any other document? Thank you!