Select the Bow layer and Ctrl/Left Click on the icon in the Layers palette.
You have now selected the bow and there will be a row of ‘marching ants’ around
the edge of the bow.
Select/Inverse
This will reverse the selection, selecting all areas outside the bow.
Next select the ribbon layer in the layers palette.
Click on the eraser tool and using a round hard brush erase the areas of ribbon that you want to remove.
Once you have erased all the areas of ribbon that you don’t require you will now have a ribbon that looks like it has been tied into a bow.
There are probably more things that you can do to make it look realistic e.g internal
shadows and using the dodge and burn tool to give the ribbon a few more wrinkles.