Попробуйте ниже -
update a set a.col4=b.col4 from dummy_jd a
join
(select col1,col2,col3,col4,col5,sum(reported_amount) reported_amount
from dummy_jd_2 where col5=3843 and col3='abc' and col1=4 and col2=3002
group by col1,col2,col3,col4,col5
)b on a.col2=b.col5 and a.col4=b.col3
where a.col1=9