Refund of tds adjustment against old demand

My tax refund for AY 2018-19 was adjusted against outstanding demand for AY 2009-10, and reduced' refund received.

I approched my ITO through email and submitted details of missed out TDS for AY 2009-10 and got a response that missed out TDS from my employer is considered and following response received.

"The demand for A.Y. 2009-10 of RS. xxx/- has been reduced by giving credit to TDS from salary which was not given credit earlier.   Consequent to this you may approach CPC and claim refund for A.Y. 2018-19''

Can anybody advise me what step I should take to claim my refund.