You cannot put a 2019 tax document on a 2020 tax return. It can only be put on a 2019 tax return---so you can amend your 2019 tax return to include it if you think it will change your 2019 return. Is it a 1098 for mortgage interest? Did you have enough itemized deductions to exceed your standard deduction---or would adding the 1098 help you to cross that threshhold?
Or is it a 1098T for tuition, a 1098E for student loan interest you paid in 2010?
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