What exactly do you need? If you prepared a 2018 online return with TurboTax, you should be able to retrieve a 2018 PDF of your return or tax data file if needed. TurboTax does not have a copy of transcripts. Transcripts are abridged versions of returns, which are only available from the IRS. Is that what you need, or are you using the wrong term?
If you want a copy of your online 2018 return PDF, log in and in the left column menu click on "Previous Taxes". Then choose tax year 2018 and "download/print the PDF." If the 2018 return was prepared in Free Edition and access is locked, we can tell you how to pay for an upgrade to unlock it (19.99 for PLUS).
If you log in and can't find any evidence at all of the 2018 return under "Previous Taxes" or "Your Tax Returns & Documents", then you may have multiple accounts and signed into the wrong one. We can help you find the right account.
If you do want a transcript instead of the actual return, here's how to get one. If you qualify to open an IRS account, you can download a free tax return transcript from the IRS. If you can't download one, a transcript by mail takes 5-10 calendar days.
http://www.irs.gov/Individuals/Get-Transcript