How to correct mistake in mvat challan

Pratik khilari (CA FINAL) (75 Points)

20 February 2015  

Dear Expert,
While making mvat payment for the oct to dec,14 quarter , my staff was wrongly
entered the period in the challan and we had already filed our mvat returns.
Now i came to know the mistake done by my mistake.
Please tell me know how to rectify this mistake??
To whom shall i approach? bank or Sales tax dept?