My name is Haripriya Vijayvargiya and my DOB is the 5th of February , 2004 How can I join Indian Air Force as a girl ?

Hello Haripriya,
NDA or National Defence Academy Exam is a national level exam organized by UPSCALE to recruit candidates in Army, Navy and Air Force. It is a two tier exam where candidates have to quality the written test as well as SSB Interview rounds.
The age limit for applying is 16.5 - 19.5 years. Only unmarried candidates can apply.
Since you are 15 years old you cannot apply this year. You'll be eligible next year for the November session.
To know more details of the eligibility criteria please follow the link below:
https://competition.careers360.com/articles/nda-eligibility-criteria

Hope this helps.
All the best