Composite to Regular Scheme Conversion

Hi,

Firm was registered in the second quarter under composite scheme and bill raised to customer showing as total bill value. Filing done in composite scheme in 2nd and 3rd quarter, but customer is asking for their input credit, explained to the customer but not accepting. Hence, would like to change from Composite scheme to regular scheme. Is it possible to change from 2nd quarter in regular scheme and do revised return or else i can make changes only in 4th quarter. Please guide, what to do....

Regards,

Mallika.P