Hello Sanchaya!!

I assume that you are asking your query regarding the NEET application, as you didn't specify about the name of the application form.

In NEET application form, there are 7 codes in which you have to select one. As you have completed 12th from Tamil Nadu stateboard in 2016 and have not joined any course, you come under the category of Repeater/Dropper.

So, you can select code 2 in the application form. For your further references, you can also go through the below link.

https://www.google.com/amp/s/medicine.careers360.com/articles/neet-qualification-codes/amp

Best of luck !!