So, you understand what "carried forward" losses are.
"Carried Back" is the same thing, but you claim the capital losses on an earlier year. As you point out, you can claim $3000 capital loss against ordinary income each year. So normally, if you have a $30k loss with no offsetting gains, then you may end up claiming that over ten years. But Section 1256 losses can be carried back, as well as forward; so you can distribute some of the loss to years you've already done.
Presumably, you've already filed for the previous years; so you essentially amend the previous filings to include the carried back losses. You usually file Form 1045 rather than 1040X for the previous years.
For example, if in 2022, you had a $30k loss, you could allocate $3000 each to 2021, 2020, and 2019, and either net those against gains or against ordinary income. You file Form 1045 for each of these years, and get a tax refund due to the decreased tax. You would take $3000 against ordinary income for 2022, and then you have only $18k to carry forward.
That's the gist anyway. There are lots of restrictions on how much you can carry back. It's kind of an advanced move, so unless you have enormous losses in futures contracts, or feel like doing a lot of paperwork, maybe just leave the carryback at zero. See the IRS instructions for Form 6781 for details.
