On your 2020 tax return, the converted new IRA should have caused a tax deduction since you contributed taxed income to a traditional IRA. The money in the new traditional IRA is now untaxed. If you forgot to take this deduction, then I guess file an amended 2020 return. If you ended up contributing too much to your traditional IRAs in 2020, I think you just lose but I'm not sure.
Investopedia has some info as well.
