You have to calculate the amount of the fellowship money that you actually received before your 2nd anniversary date. The institution paying the fellowship may do this for you, or you may have to do it yourself, based on your bank statements or statements from the institution. Second, you have to report the result on form 1040. For instructions on how to do this, see the instructions in publication 519, section titled "Students, Apprentices, Trainees, Teachers, Professors, and Researchers Who Become Resident Aliens", subsection "How to report income on your tax return." In the 2017 pdf of the publication it's on page 48. Hope that's helpful.
