I want to re-file my 2018 Tax Return. What's the best way to do ?

What did you use?  Did you use Turbo Tax Desktop program or somewhere else?

IF you did not use Turbo Tax,

For prior years you have to buy the Desktop program.  You can only buy the download for prior years.  You have to buy a separate program for each year.  They only sell the last 3 years.  You need a full Windows or Mac computer to install it on.  Buy the download here   

  https://turbotax.intuit.com/personal-taxes/past-years-products/

If you don't have the original.tax file you have to first recreate the actual wrong original return.  You can use the Forms Mode.  Then when it matches each line that you really filed you have to tell Turbo Tax you will mail it so it thinks it was filed.  Then you can amend it.

How to amend a 2018 Desktop return,

https://ttlc.intuit.com/community/amending/help/how-do-i-amend-my-return-in-the-turbotax-cd-download-software/00/27578