What signature date should I use to e-file an amended tax return for 2019? (TTX limits end date to 12/31/20)

I wish to e-file a 2019 amended return in TurboTax. I e-filed the original return last year (March 2020) and completed the steps to prepare my amended return in TurboTax this year (March 2021). But TTX does not accept the current date as my signature date and notifies me that "TurboTax e-filing closed for the tax season on Oct. 15, 2020." The IRS site says it supports e-filing for amended 2019 and 2020 returns. Does TurboTax support e-filing amended returns or not? Is there a workaround for the signature date issue? Thank you in advance for any help.