Where to file input tax details of stock as on 30th june-17

Please let me know where to file the excise details of stock i did hold on 30th june 2017. I am really stressed about how to avail the credit of excise duty i paid on such stock. I paid excise duty at 12.5% on previous stock that i hold. I have all necessary invoices and documentation providing details of duty paid.

I heard that GSTR 3B is available to file. Do i need to mention such pre GST tax details there or is there some other form?