You will not receive a refund for a 2018 return now. It is too late. Even if your 2018 tax form shows a refund, you have forfeited the refund. The IRS will keep it. Sorry.
Online preparation and e-filing for 2018 and 2019 and 2020 is permanently closed.
To file a return for a prior tax year
If you need to prepare a return for 2018, 2019 or 2020 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/
You may also want to explore purchasing the software from various retailers such as Amazon, Costco, Best Buy, Walmart, Sam’s, etc.
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.
Federal and state returns must be in separate envelopes and they are mailed to different addresses. Read the mailing instructions that print with your tax return carefully so you mail them to the right addresses.
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.
The phrase " you snooze you lose " comes to mind ... the IRS only gives you 3 years to file for a refund or you forfeit it. The refund for 2019 will be forfeited 4/15/23 so if you have not yet filed the 2019 return get hopping.
TurboTax for 2018 is no longer available or supported. If you want to file for 2018 even though you will not get the refund, you will have to look for other tax software that is still available for 2018. You could download the blank forms and instructions from the IRS web site and fill them out by hand, but I don't recommend that. Unless you are experienced at preparing tax returns on paper, it's too likely that you will make mistakes.