It sounds like you prepared a 2019 tax return with information for 2018. If so, you will need to amend your 2019 tax return to correct the amounts reported to only reflect 2019 activity.
See the attached link for instructions to help you amend your return.
For your 2018 tax return, you will need to prepare it using the software for 2018. You can use the following link to download the software to prepare your return.
Make sure the year on your source documents, (W-2 forms, 1099 forms, etc) also reflect the year of the tax return you are preparing to ensure the items match what has already been reported to the taxing agencies.
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If you still need to file a 2018 return. You can only buy the download for prior years. You have to buy a separate program for each year. They only sell the last 3 years. You need a full Windows or Mac computer to install it on. Buy the download here
You have to print and mail prior year returns. When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS received the return. Don’t forget state.
Important! Mail Federal and State in separate envelopes and mail each year in separate envelopes.
Or If you have a simple return You can fill out the blank forms for free.
Here is the IRS 2018 Form 1040
And 2018 Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2018.pdf
2018 Tax and EIC Tables https://www.irs.gov/pub/irs-prior/i1040tt--2018.pdf
IRS 2018 Schedules 1 thru 6 (only if needed)
Sch 1 : https://www.irs.gov/pub/irs-prior/f1040s1--2018.pdf
Sch 2 : https://www.irs.gov/pub/irs-prior/f1040s2--2018.pdf
Sch 3 : https://www.irs.gov/pub/irs-prior/f1040s3--2018.pdf
Sch 4 : https://www.irs.gov/pub/irs-prior/f1040s4--2018.pdf
Sch 5 : https://www.irs.gov/pub/irs-prior/f1040s5--2018.pdf
Sch 6 : https://www.irs.gov/pub/irs-prior/f1040s6--2018.pdf