Open up the file in FSX\PMDG\PMDG 777X called "777X_options.ini" - look at the bottom, there should be a line that says StartupPanelState=. If there's anything there after the equals sign like 777 SHORT or 777 LONG, delete it and save the file.
I had the same problem and it restored it back to the default setting and I was able to fly the tutorial.