The July 15, 2020 date is only for those that have taxes owed and need to pay those taxes by that date to avoid a failure to pay penalty. For a tax refund there is a 3 year time-frame to file for a refund. So for tax year 2019 a tax refund can be filed at any time on or before July 15, 2023.
See this TurboTax support FAQ for the procedure to use when the non-filers website was used and a 2019 tax return needs to be filed - https://ttlc.intuit.com/community/tax-topics/help/stimulus-how-to-file-your-return-after-getting-rej...
