Hey Arjun'

You need to mention the name of the form in which you want to change your basic details. In most of the forms they have provided an option as transgender at the time of  form filling but if they did not or if you have ticked some other catehory by mistake then it's not a problem as you can sort it out at the time of counselling.

I hope I got your question right but if I did not then please mention the name of the form in the comment section and I will look into how to do corrections in that respective form.