How to sum up values in data driller

The data driller does not provide for a Group By clause (it provides
for columns, where and order by)

But you can trick it to provide for a group By:
To do this, use the "Where" clause. Give a dummy where and then add
GROUP BY

Example for armast to group by sales person

In the Where clause give : custno = custno GROUP BY salesmn

Your SQL select would be

SELECT <fields you have chosen> ;
FROM <armast> ;
WHERE custno = custno GROUP BY salesmn ;
....
The custno = custno is to satisfy a valid where clause and then the group by.

P.S.: I haven't tried this myself recently, so you might have to tweak
it more than what I have mentioned here.