What form of business entity? Are you using TurboTax Business?
You cannot, obviously, transfer your 2018 return into TurboTax for 2019 since the 2019 version has not yet been released (and will not be until probably November).
What you can do is save your 2018 tax file (i.e., back up the .tax2018 file), create a new return based on that return, and make the appropriate changes for 2019. Be advised that you will have to print and mail the return since the 2018 program will not accept dates that begin in 2019 and, as a result, you will have to write, by hand, the appropriate dates on the forms.
You can try doing that, but I doubt the file will transfer back in the 2018 version.
Rather, it will probably read the file as having been created in the 2018 version of TurboTax.