The bewildering variation in the number of different places French airports seem to hide their flight planning facilities is a constant source of annoyance I find.
The most common arrangement though is a simple telephone usually placed near to where the big yellow 'C' symbol is which usually has a direct line to the regional flight planning office. However I have encountered everything from absolutely nothing to the aforementioned Olivia system in various places. The safest option since it gets you talking to a real human being is to have the number of the regional flight planning office so that you can always call them if technology defeats you.
At Le Touquet you shouldn't have a problem, have your return route written down and then if it isn't obvious just ask someone were the computer terminal or phone is to file it.