Best guess--you used the non-filer site to get a stimulus check?
If you used the IRS website for non-filers to request a stimulus payment then a 2019 tax return was filed with your name and Social Security number. If you are now filing a 2019 tax return it will be rejected since the IRS has already received a 2019 return with your name and SS number.
See this TurboTax support FAQ for how to proceed if this is your situation - https://ttlc.intuit.com/community/tax-topics/help/stimulus-how-to-file-your-return-after-getting-reject-r0000-902-01/01/1602609
If you did not use the IRS website for non-filers and the IRS is rejecting your tax return for a SS number, then someone has already filed a tax return with your SS number entered either as a dependent or the taxpayer. You will not be able to e-file your tax return, it can only be printed and mailed.
See this TurboTax support FAQ for printing a tax return for mailing - https://ttlc.intuit.com/community/printing/help/how-do-i-print-and-mail-my-return-in-turbotax-online...