Income tax refund

 For rectifications in challans paid through online mode (internet challan) , taxpayer may contact their concerned Assessing Officer (AO).

EX- EMPLOYEE OF MY FIRM WRONGLY PAID SELF ASSESSMENT TAX FOR A WRONG PAN.  THERE IS A WORD FILE IN THE SYSTEM ADDRESSED TO AO FOR CORRECTION OF PAN. I DONT KNOW WHETHER SHE MAILED OR POSTED IT

https://www.incometaxindia.gov.in/Documents/challan-correction-mechanism-26082011.htm

First you have to send letter to the A.O. for giving credit. Once the tax credit is correctly reflected on your 26AS, you will have to rectify your return.