Remove vertical trim board, place wooden form where exterior face of added concrete is to be, pour concrete/mortar, let set up hard, remove form, replace trim board.

I'm not a pro but would like to offer some advice in regards to filling that area between your foundation and brick veneer: before proceeding, you may want to determine if an air gap should be maintained between the brick and the newly-installed cement.

What you show is not an air gap as tendrac suggests, it is poor planning and execution, it needs be closed up to keep critters out. The remainder of the brick installation has the normally present air gap.

thank you both for the comments....we have reached out to the builder several times and he is yet to have it fixed.

You should get some non-shrinking grout to fill that. you can stir it up with a VERY little water -and like a sand castle - get it to pack in there. Using a board as a form will leave it smooth - and you'll want something to jam in there to push the grout against - something like backer rod (or a pool noodle or even a ballon!)