You need to file separate 2017 and 2018 returns--do not try to combine those tax years in any way.
To file a return for a prior tax year
If you need to prepare a return for 2016, 2017, or 2018 you can purchase and download desktop software to do it, then print, sign, and mail the return(s)
https://turbotax.intuit.com/personal-taxes/past-years-products/
Remember to prepare your state return as well—if you live in a state that has a state income tax.
When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s. Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS/state received the return.
Note: The desktop software you need to prepare the prior year return must be installed/downloaded to a full PC or Mac. It cannot be used on a mobile device.
If you are getting a refund, there is not a penalty for filing past the deadline. If you owe taxes, the interest/penalties will be calculated by the IRS based on how much you owe and when they receive your return and payment. The IRS will bill you for this; it will not be calculated by TurboTax.
https://ttlc.intuit.com/questions/1900990-how-do-i-file-a-prior-year-tax-return
you have to file using the tax software from those years and the associated W-2s. Check with Intuit to see if those packages are still available. An alternate is to go to www.irs.gov and then to forms and instructions, and search for 1040 forms from the associated years.
If all you have is w-2 income, then it is very straightforward to file. Potential good news is that if you don't own taxes, then there will be no penalty or interest, and you will get any refund due (but with no interest), and you no longer have to worry about being caught by the IRS. Potential bad news is that if you do own the IRS then there will be associated penalty and interest on the amount you own, but it will only get worse the longer you wait, so do it as quickly as possible.