Sorry to know this! Now the first thing you have to do is to file a complaint at your nearest police station that you have lost your document. Now the copy of the complaint you have to take to your school/college you have studied in. Now they can give you some guidance as per the rules and regulations of the board you had studied in. Also you can find out the contact details of your board from Google and you can ask the officials there, they will help you out.

**Specific procedures can't be concluded by us because firstly you haven't mentioned your board, secondly the rules are changing, so its better to get the updated rules.

I hope this answer helps. All the very best for your future endeavors!