Hello dear candidate,
As the NCHM JEE 2020 counselling has already begun and you have appeared in the exam too under the same category, you cannot now change your category because opening and closing ranks for different categories in various participating institutes are different. However you can still mail the NCHMCT regarding your issues over the address given on official website.
There is no provision of making correction in the registration form for counseling process of NCHMCT JEE. Still you can try by sending a mail regarding your concern and hopefully they will help you out.
I hope this helps.