Hello,
Please copy over all the *.tt17 tax files which usually is present under your "Documents --> TurboTax --> 2017" directory. You can create a similar directory structure on your new machine or you can place these documents at any other location.
In case you copy it to the same location as mentioned above TurboTax will automatically show these documents so that you can carry forward, else you can browse to those files to jump start your 2018 return.
Hope this helps!