Notice U/s 143(1)a Outstanding demand

Sumit Jaicky (13 Points)

13 June 2018  
The demand is of AY 2012 - 13 where rectification right with AO.
The demand for that year was already paid by employer in that year which is showing in 26AS also.
How to submit response to it.. Can I do online then how or I have to go to AO for that. And within which time period I have to resolve this matter.

Sumit