If you completed your 2020 tax return using TurboTax Online, refer to the following Help Article to obtain a copy of your return: How do I access a prior-year return?
For returns completed using the TurboTax CD/Download software, you would have needed to save the .tax or PDF file to your computer or drive of your choice. If you didn't save a copy but you still have the CD or download of the software from that year, follow the steps listed here: How do I access my prior-year return?