There are 10 Centres that have been identified for issuing PWD certificate for 50% All India Quota and Central Universities and Institutions. One of them is Madras Medical College. Page 73 of https://www.digialm.com/per/g01/pub/1258/EForms/image/pdf2/Information_Bulletin_NEET_MDS_2020.pdf has the template. You need to visit Madras Medical College and ask for Disability Certificate Board department or anyone from that department who issues those Certificates. The Board will conduct various tests and assess you based on the regulations. You can meet the Medical Superintendent who can help you with the process.