Did your 2017 income actually get filed and accepted as a 2018 return? If it did then you need to mail in a 1040X Amended return to change the wrong 2018 return to be for 2018. And then you still need to file an original 2017 return.
If you have a simple return You can fill out the blank forms for 2017 for free.
Here are some blank forms & instructions for 2017
1040 https://www.irs.gov/pub/irs-prior/f1040--2017.pdf
Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2017.pdf
1040A https://www.irs.gov/pub/irs-prior/f1040a--2017.pdf
Instructions https://www.irs.gov/pub/irs-prior/i1040a--2017.pdf
1040EZ https://www.irs.gov/pub/irs-prior/f1040ez--2017.pdf
Instructions https://www.irs.gov/pub/irs-prior/i1040ez--2017.pdf
2017 Tax Tables https://www.irs.gov/pub/irs-prior/i1040tt--2017.pdf
Publication 17 Tax Guide for 2017 https://www.irs.gov/pub/irs-prior/p17--2017.pdf
Don’t forget your state. And you will have to print and mail your returns. So be sure to attach copies of your W2s and any 1099s that have withholding on them. You have to mail federal and state in separate envelopes because they go to different places. Get a tracking number from the post office when you mail them for proof of filing.
