Partnership firm has filed its itr as proprietorship

Hello friends.. I am a banker and branch manager in a public sector bank. One of our borrower was the partnership firm but it has filed its ITR for AY 2017-18 (ie for March 17) as proprietorship firm. Earlier before taking the working capital finance from the bank in March 2016, the constitution of the firm was proprietorship but while availing the finance it was converted to partnership and the change was made with DIC. Accordingly we financed the partnership firm. But the borrower did not made any change in the VAT / CST registration and in the records of VAT department the firm is still a proprietorship firm. On this basis the borrower obtained GST for proprietorship firm only and filed the ITR also as proprietorship. Now the borrower is forcing us to accept the balance sheet of proprietorship firm. So whether there is any way to 1. change the partnership firm in proprietorship. 2. modify the ITR filed from proprietorship to partnership. 3. Any other legal complications