If you used TurboTax Online for 2018 see the FAQ at the following link for instructions to access the tax return.
How do I access a prior year return?
If you used the CD/Download TurboTax software for 2018, see the FAQ at the following link. In the FAQ, click the blue link that says "I use TurboTax CD/Download."
How do I access my prior year return?
