This page:
https://www.nrjmobile.fr/visiteur/moncompte.html
suggests you can do it from your personal web page. I assume that's the same as 'your VIP space' (top right) - it looks like you should have received an access code for that.
I can see no mention anywhere of any special codes to access it from the phone. The only one I found was 123 for voicemail (which costs). (Edit: No - it's free in France, it costs from abroad.)
Dave