You cannot get a job in Sapcex directly. Leave Spacex, even ISRO is difficult. Let me explain you the process.

First you need a Undergrad Degree from a topmost University like IIT's in Aeronautical or Mechanical Engineering. Then you will have to apply for MS in MIT or Harvard as almost all the Scientist or Engineers in Spacex are from these Univ. only. The Heavy falcon Mission was Engineered by a MIT Grad only.

Then after your MS you will have to wok in any smaller firms for few years and then as per your talent you will be selected or you will have to apply.