Please explain what you mean by "re-file my 2018 return." Was it ever filed successfully and accepted? Or has it not ever been filed? Was it rejected last year? What happened? What are you trying to do?
As for amending 2019---wait until the 2019 return has been fully processed. Do not amend if it is still being processed.
How do I amend my 2019 TurboTax Online return?
A 1040X cannot be e-filed. It must be printed and mailed. It will take about 4 months for the IRS to process an amended return. It is a good idea to use a mailing service that will track it, like UPS or certified mail, so you will know it was received.
Wait about 3 weeks from mailing and you can check the status of your amended return:
https://www.irs.gov/Filing/Individuals/Amended-Returns-(Form-1040-X)/Wheres-My-Amended-Return-1
https://www.irs.gov/filing/individuals/amended-returns-form-1040-x/amended-return-frequently-asked-questions
https://ttlc.intuit.com/questions/1908543-do-i-need-to-amend