Wrongly I have paid Cash under wrong head i.e. CGST instead of IGST. How can I get cash back... can I file refund application? Kindly guide

Reply:- In terms of Section 54 (1) Any person claiming refund of any tax and interest, if any, paid on such tax or any other amount paid by him, may make an application before the expiry of two years from the relevant date in such form and manner as may be prescribed: [See Rule 89]

So, you can file RFD 01 application for refund.

Further, you can use Form PMT 09 for transfer of amount from one head to another head.