The IRS says not to file another tax return if you have already filed by mail.

I filed my 2019 tax return by mail on 2/13/2020 and I haven't received my Federal Tax Refund.  The IRS is not open for phone calls. What should I do?

No.  Do not efile or mail it again.  

They just started opening the mail in June that's been stacking up. So you have to keep waiting.

See this IRS page for the latest information

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue

You should be patient and wait as during the lock-down the IRS did not process mailed in returns. You must not filed again, not by mail, not electronically.

This IRS document outlines IRS operations during Covid-19 times.