On a screened porch addition, the contractor placed the support beam vertically against the siding and there are gaps-how to fill in gaps

[Joanne]

Suport beam in against the siding and so there is a gap where the board does not touch or cover the indentations of the siding. Is there such a thing as a board that is cut to conform to the siding or must I fill in with some sort of caulk. Not sure I am explaining this correctly. Don't know what to do. thanks