I need to file my 2019 taxes, where do I start?

You need to use a desktop (CD/Download) version of TurboTax.

See https://turbotax.intuit.com/personal-taxes/past-years-products/2019

Online versions are not available for the 2019 tax year.

How to prepare a prior year return

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-prepare-a-prior-year-tax-return/00/25984

How to finish a return you started online

https://ttlc.intuit.com/community/prior-year-return/help/how-do-i-finish-a-prior-year-return-that-i-started-in-turbotax-online/01/26322

To do a prior year return you have to buy the Desktop program here,

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

You will need a full Windows or Mac to install it on.

If you paid for the Online version you can ask for the 2019 Desktop program.

If you have a simple return and want to file 2019 for free you can fill out the forms by hand.  Here are some basic forms.....

Here is the 2019 1040 return

https://www.irs.gov/pub/irs-prior/f1040--2019.pdf

or if you want bigger type use 1040SR for Seniors,

https://www.irs.gov/pub/irs-prior/f1040s--2019.pdf

2019 Instructions https://www.irs.gov/pub/irs-prior/i1040gi--2019.pdf

2019 EIC and Tax Tables https://www.irs.gov/pub/irs-prior/i1040tt--2019.pdf

2019 Schedules 1-3

https://www.irs.gov/pub/irs-prior/f1040s1--2019.pdf

https://www.irs.gov/pub/irs-prior/f1040s2--2019.pdf

https://www.irs.gov/pub/irs-prior/f1040s3--2019.pdf

Don’t forget your state.  And you will have to print and mail your returns.  So be sure to attach copies of your W2s and any 1099s that have withholding on them.  You have to mail federal and state in separate envelopes because they go to different places.  Get a tracking number from the post office when you mail them for proof of filing.