Hello student I request you to please help me with the entrance examination name which you're talking about so that I can check and provide you the exact information. If you're talking about NDA entrance examination then you can't fill the application form today. Upsc will release NDA application form on 10th of June and last date will be 30 june so you can fill the application form in the month of June.

Feel free to comment if you have any doubt

Good luck