Living in IL for three months of 2020 is not relevant to your 2019 tax return. If you are working on a 2019 tax return you put information about 2019 on it. The only IL fact you had better use on the tax return is your current address so that they IRS knows where to send mail to you.
Un-fortunately...you've started a second post where it's not clear what your situation is in this one...you need special help for resident or non-resident aliens (I think)...so go back to your initial post. Most of us in this PUBLIC forum are not particularly conversant about alien tax filings...but you have a TTX representative in the other post who may respond with more information.......eventually.
You need to work thru your initial post, and ask any additional questions there as added comments.
GO and work only at this other post: