Sorry, to say you but after completing 12th you can’t join ISRO for that you must have graduate degree of technology then only you will be eligible for that.

B. Tech Bachelor of Technology
Duration: 4 Years
Level: Graduation
Type: Degree

Eligibility:
Candidate must have 12th passed certificate from a recognized University with the PCM subjects.

After completing B. Tech you can join ISRO through GATE exam.

Here I am giving you some B. Tech colleges in India:

Indian Institute of Technology, Madras
Indian Institute of Technology, Kharagpur
Indian Institute of Technology, Kanpur
Indian Institute of Technology, Delhi
Indian Institute of Technology, Bombay
VIT University, Vellore
Thiagarajar College of Engineering, Madurai
Thapar University, Patiala
SASTRA University, Thanjavur
Punjab Engineering College University of Technology, Chandigarh
PSG College of Technology, Coimbatore
Netaji Subhas Institute of Technology, Delhi
National Institute of Technology, Warangal
National Institute of Technology, Tiruchirappalli
National Institute of Technology, Surathkal
National Institute of Technology, Durgapur
National Institute of Technology, Calicut
Manipal Institute of Technology, Manipal
JNTU College of Engineering, Hyderabad
Jadavpur University, Kolkata
International Institute of Information Technology, Hyderabad
International Institute of Information Technology, Bangalore
Indian School of Mines, Dhanbad
Indian Institute of Technology, Ropar
Indian Institute of Technology, Roorkee
Indian Institute of Technology, Hyderabad
Indian Institute of Technology, Guwahati
Indian Institute of Technology, Banaras Hindu University, Varanasi
Indian Institute of Engineering Science and Technology, Shibpur
Delhi Technological University, Delhi