How can I change my 2019 tax return by using Refile, as there is a T4 slip duplicated and also some incomes to be entered under T1 Adjustment? I already received my NOA.

[TurboTaxKim]

If you have NetFiled your tax return and received your Notice of Assessment (NOA), you should be able to do a ReFile from within TurboTax itself. 

• If you used the Online version of TurboTax, a button next to the filed return should appear giving you the option to Refile.

• If you are using the CD/Download version of TurboTax and have it installed on your computer, the procedure to ReFile is a little different.
  
  When you first open up TurboTax, scroll down past your returns and you will see a button on the right-hand side that says "Change a filed return". This will then lead you to a pop-up window where you can choose the return you wish to make the adjustments too.

Please see the attached screenshots.