If you used TurboTax to file your 2017 tax return as well...

2017 tax information from TurboTax which has it

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If you used TurboTax to file your 2017 tax return as well, you can log into your account and select the "Previous Taxes" link on the left hand side of the "Tax Home" screen.

If you used a different service to file your taxes last year, you can either reach out to that service, or you can request your tax transcript directly from the IRS using this link:

https://www.irs.gov/individuals/get-transcript