Hello Maneesha, 

You can appear for NEET as many times as you wish, provided you stay within the upper age limit. 

As long as you haven't attained the age of 25 (30 if you are reserved category candidate), you can appear for NEET as many times as you wish.

For more detailed information you can refer to this website -

https://medicine.careers360.com/articles/neet-number-of-attempts-and-age-limit