The University is using an online platform for the pre-registration: eCandidat. 
You have to create an account for using it, and you will need the following information: 
- if you are already a student in France, your personnal INE (or BEA, or INA)
- a valid email address
- all information concerning your studies and academic cursus
- all information concerning your professional activities 

Once your account created, you will have to enter these information in one of the 7 links on the left menu, in text, and you will have to download documents in PDF. 

Concerning the last step ("Candidatures", meaning "Application"), you will find the Master "Computer Science for Aerospace" under the "Faculté des Sciences et Ingénierie - MASTERS mention informatique", and then, depending if you apply for Master 1 or Master 2, under LMD/Master 1 or LMD/Master 2.