Hi Alexis. You need to make a new face on the surface of your beam by using '/Insert/Curve/Split Line' (think I've got that right) after drawing the shape you want using a sketch. This sketch can be open or closed, depending on the shape you need (i.e. it could be a line across the width of the beam that splits, say, the top surface in two). I expect you need a circular area or similar to enable you to apply a load over a specific area as per your post.
I'm not at a SW PC right now so can't show you an example, so have a look in the help for the Split Line feature. If you're successful, you'll be able to apply your load to your newly-created face by selecting just that face for your load in COSMOS/Simulation. There's no need to create a new surface. There should be a load of topics posted about Split Lines to create new faces.