Thank you @Anonymous, your solution makes sense, I will go with it.
I file 2019 tax using corrected capital loss carryover, so that all my taxes, past and future, are correct.
And I don't do anything about amending 2018 return, unless IRS requests it. The case now boils down to them not having corrected form, but having correct 1040 filed and correct taxes paid. If they decide they need the form for 2018, they will send me a notice and I will comply. The $ difference is not significant (IMO of course), and the correction is in their favor.
Since brokerage reported them this info as well, they technically should have all corrected numbers already.
Thanks for taking time to help!
