Contributing to Traditional IRA for Previous Year
I have already filed my 2019 taxes back in February 2020, but recently opened a Traditional IRA. Since the deadline has been extended to July 17, 2020, I decided to contribute the full $6,000 for 2019 into my Traditional IRA, instead of 2020, and will contribute $6,000 towards 2020 sometime in the near future.
Since I've already filed my 2019 taxes, how do I amend it to update my tax deductions?