if you are not required to file in 2019 and your question is really about getting the stimulus... just file the 2020 tax return in the coming months.
The way this REALLY works is EVERYTHING is based on you 2020 income, filing status and number of children under the age of 17. What these numbers were in 2018 and 2019 does not matter.
The IRS will calculate your stimulus based on 2020 numbers; that is what is considered the ACTUAL.
The two payments were just ESTIMATES
if the ACTUAL is greater than the ESTIMATE, you will receive that amount as a credit on your 2020 tax return.
if the ESTIMATE is greater than the ACTUAL, you are not required to return the money nor does it impact your refund. Line 30 on Form 1040 will be zero.
