How to make rectification?

Anyone can guide??

In the assessment year 19-20, Regular assessment tax had been paid under wrong head of self assessment. AO corrected the minor head of tax pmt & now tax amount is reflecting in 26AS correctly. But demand is raising still for such amount.

I used common offline utility for rectification but there is option of tax only on self assessment basis not for regular assessment.

How to get the demand nullified? What procedure to follow further?