If I didn’t finish fileing my 2018 tax return and the IRS says they do not have it, can I complete and file it by using the “Amend” program on TT?

NO.  Amending is a special process you only use for a return that has been filed, accepted, and fully processed by the IRS.  Your return was not filed, so you do NOT click on anything that says "amend" for it.

Instead what you must do is download the 2018 desktop software to finish preparing it and then print, sign and mail it.

 Online preparation and e-filing for 2018is permanently closed.  You have to download 2018 software to a full PC or Mac (not to a mobile device) and then print, sign and mail your return.  If you already paid for your TurboTax software, you can contact customer support to push a download of the software to you.

To call TurboTax customer support

https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number

They are available from 5 a.m. to 5 p.m. Pacific time.

To finish a prior year return started in TT online:https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb

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 and/or your state received the return.

If you never filed your 2018 tax return you cannot/have nothing to 'amend'.  You can only 'amend' a return that the IRS has already received from you.

If you started  an On-Line return and simply never finished it;  you will have to log into your TTax On-Line account and download he return to your PC as a .tax2018 datafile (you should also download a copy of your return as a .pdf file so that you will have something to refer to.  You will then have to purchase a copy of TTax2018 (CD or download) and install it on your own PC.  Copies of last year's TTax program a still available at on-line retailers and from TTax:

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

Once you download your .tax2018 datafile save it to the default location TTax prefers (C:\My Documents\TurboTax).  The after you install TTax2018 and launch it TTax should find the file on your PC.  If it does not find it automatically you can click the blue 'Locate File' button and TTax should be able to find the file.  At that point you can continue preparing your return from where you left off.

Since it is too late to e-file a 2018 return you will have to print and mail your return. 

Also, when mailing tax returns it is a good idea to mail the returns 'Certified' with 'Return Receipt' so that you will have proof and tracking of submission.