GST reversal of GST excess ITC taken

One of my client has taken ITC on manual basis in April month because his client has not filed the return in time (13 April ) which lead to non reflection in GSTR-2B.because of which he was required to pay 1.2lakh GST even thought Actully he was not required to pay gst. now in this month those bills are showing in gst 2B. how to reverse ITC in 3B or DRC-03?