Yes, you paper file it.
You can only efile ONE return per year per FEIN.
Print to paper & manually change the dates, or print to PDF & change dates using Adobe (a much more professional looking product...)
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If at all possible, you are better off filing an extension and wait for the 2020 software.
If you use the 2019 software, you would need to override everything to correspond with 2020 tax law. But unfortunately, Congress is well known for not finalizing the current year tax law until at least December. While there may not be too many things affected on a Partnership return, you would still need to be aware of any changes.