You will file it just like it is not late. The only thing is, if you owe, you may get a penalty for filing late if you have taxes due. If you are getting a refund, then there is no penalty.
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If you haven't started yet then online is closed. If you want to file for free you can fill out the forms by hand. Here are some basic forms…..
Here is the IRS 2019 Form 1040
or if you want bigger type use 1040SR for Seniors,