It should be able to find the .tax files wherever they are. If it doesn't find it there is a Browse button so you can navigate to it.
Did you try double clicking on the .tax2018 file to see if it opens in the program?
One thing to know.....
After you get the program installed the first thing to do before you open your tax return is to update the program and install any state programs you had. Then open your file. So you first might need to start a fake return to be able to download the state program (go to FILE - NEW TAX RETURN)
Then go to FILE -Open and find your return.
