I ran into the same problem. After reading/searching the manual, I read some threads on here and found an answer that worked (pressing zero). The tutorial is from an older version of 3dgs. At least I'm guessing it is as the dialog boxes are nowhere near the same.
If you feel it's a big deal though, maybe an email to the tutorial's creator for an update is in order? Personally I don't mind doing some research to find out things like this. Since I'm totally new to 3dgs, just about everything I read teaches me something new. I discovered several things in just trying to find out how to enter "fly-thru mode".