A separate tax return must be filed for each tax year including only the income and expenses for that year. You can go ahead and file your 2019 tax return using the online product.
To file the 2017 and 2018 tax returns, you must buy, download and install on your computer the tax program for each of those tax years. Here is where to buy it: https://turbotax.intuit.com/personal-taxes/past-years-products/
Tax returns for prior years must be printed and mailed. They can't be efiled. You must print and mail them yourself because TurboTax doesn't print and mail them for you. The tax return for each year should be mailed separately.
Thank you for your clarification.
I just have one additional question. When I go to file my 2019 tax return electronically, won't it ask for tax information from previous years? Will it let me file my 2019 now before my 17 and 18 taxes are processed?
When it asks for your 2018 AGI, enter the number 0. That will allow the IRS to accept your 2019 tax return. The same thing would be required if you filed your 2018 tax return first because the 2018 AGI would not be in the IRS database.