Retirement tax questions

Thank you! When I amend the 2018 taxes, will I owe more taxes for that year, or will it be a wash after I do 2019 taxes? Do I send only form 8606 or do I need 1040+everything again? Should I wait a few weeks after the amendment before filing 2019?

 

I plan to make the 2020 contribution late this year to get back on track. Will I need to amend 2019 returns after I do that?