It isn't an UPDATE if you want to create a new record. It would be an INSERT INTO query.
From your description, I MIGHT consider this approach.
First, write a summation query to generate whatever sum you are trying to generate. You should be able to look up SUMMATION QUERY easily enough. I'm not clear on what else might go in this query because your description is a bit limited. Summation queries resemble this:
SELECT SUM( [Customer Rate] ) AS SumRate, [Customer], ... FROM MyTable GROUP BY [Customer] ;
This would give you a query with two fields: SumRate and Customer.
Then as a second step, write an INSERT INTO (append) query to create the new record you want. Look up the syntax of INSERT INTO ...SELECT, which is the way that you would insert records based off a table or query (which appears in the SELECT clause).
INSERT INTO MyTable (list of fields to be inserted in one record) SELECT <<<list of fields to be used in the insertion>>> FROM MyNewQuery ;
NOTE that there is A LOT more to it than this. Inserting a new record into a table is perfectly permissible, but you must not neglect the other fields in the table, particularly if any of them have validation constraints. Otherwise, the INSERT would fail.
You didn't give us much of a hint as to environment because VBA is common to Office programs. However, there is one clue... You are talking "rows and columns" which immediately tells me that you are thinking about this problem as an Excel user. If this actually IS Excel, you wouldn't do it this way anyway. VBA works OK, but Excel's main user interface has a different way to do this anyway. And if this IS Access, then you SURELY would not do it this way. As TheDBGuy suggests, this might be something you would do in a report, not via a query.