Dear Aspirant, for JEE Advanced you need to have OBC NCL certificate as mentioned format on official JEE Advanced website. You can go to concerned authorities in your city/town for making it , you may take a print of just  that format as mentioned on website as reference. Then take it to office in your city/town.  The concerned authorities in office would tell you the procedure over there , having a written application ( people in office might suggest this)for same before hand might help.