Hopefully you printed it and filed it for 2018. It not, then was it ever filed? If not, you can print the forms in TurboTax 2018 and file them now. Be sure to sign and provide supporting forms such as W-2s, etc. There may be interest and penalties if you owe taxes for 2018. If you did file your 2018 taxes, then you should be able to order a copy online from the IRS. Visit:
https://www.irs.gov/newsroom/how-to-get-tax-transcripts-and-copies-of-tax-returns-from-the-irs