You can only transfer data from the previous year when you first start your tax return. So yes, you will have to start your 2018 tax return over again in order to transfer data from 2017. It doesn't matter whether you delete the 2018 file that you have already created. On the first screen when you start TurboTax, click the blue button that says "Start a New Return."
It sounds like the "TT expert" that you spoke to is not such an expert. (Was it someone in TurboTax telephone support?) You do not need the 2017 program (or software, or application) in order to transfer the data from your 2017 tax return to your 2018 tax return. All you need is the 2017 tax return data file. The file has a file name extension of .tax2017. The 2018 TurboTax program will transfer the data directly from that 2017 file. When you click the "Start a New Return" button, TurboTax will search for .tax2017 files on your computer. If it doesn't find the file, click the Browse button and navigate to where the file is.
See the FAQ at the following link for instructions to transfer your 2017 information to 2018. In the FAQ, click the blue link that says "Transfer from TurboTax for Windows, Taxact or H&R Block."
https://ttlc.intuit.com/questions/1901506-transfer-last-year-s-return-to-2018-turbotax-for-windows
