Capital Gains Carryback

I submitted my 2019 tax returns last month and had a substantial capital gains, so I had to pay taxes on it.

In 2020, I have had a capital loss on some of my investments. Am I able to use the 2020 capital losses by changing my 2019 returns now and resubmitting them or will I have to claim the losses until I do my 2020 tax returns?