If I need to file more taxes that I forgot how can I do that?

[KatrinaB]

If you need to add more income or change your 2018 return after you filed then you will need to file an amended return. You should wait to do so until the original return has been processed to avoid delays. 

Follow the directions in the TurboTax FAQ below if you need to file an amendment.

https://ttlc.intuit.com/replies/3288565

Note: You will need to mail your amended return. This type of return is not eligible for e-file. 

If you need to file a return for a prior year, then you will need to purchase prior year software to do so. You cannot e-file a prior year return. Please click the link below to select the prior year software you need.

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