Don't waste your time. I have been in three new hire classes that included CFIs, military pilots, young, and old with zero FMS experience and no one ever had an issue with it. You will probably spend an afternoon on a computer where the instructor will show you how to build a flight plan. After that, you will be able to practice on your own until you feel comfortable. You will then learn about all the extra features that aren't really important on the line. It is just like getting used to a new operating system. Sure, you can read the manual all day long, but just playing around with it for an hour will be much more productive.