If you wish to become a doctor in Army field then there are two ways to join it. The first option, After clearing NEET Entrance Exam try to get admission in AFMC, If you get selected then complete your MBBS to get into. The college provides training to under-graduate and post-graduate medical and nursing students with assured career prospects in the defence services.

The Second option, After completing MBBS from any college you can apply through Combined Medical Services Exam conducted by UPSC. You can check the exam complete eligibility with the given below link.

http://www.upsc.gov.in/sites/default/files/Notification-CMSE-2018-Engl.pdf

In case you have any other query then let me know.

Good Luck!