It can be repaired many ways. Do you know the material this is made of, I don't mean if it is plastic, like what kind is it? You want to get material that will adhere to this. Consider a urethane resin that is clear and mix red translucent dye/coloring.
In the repair process you would contain the material by placing a mold out of clay, and or clear tape with foam material. You allow some venting on the edge, which you could clean up after it cures. one supplier of products you might be interested in is smooth-on. they are out of Texas, but have multiple locations on the west coast. Alternatively, you could for more economical approach find any good clear plastic repair epoxy/resin material, and add red coloring/dye before applying it.
In summary, you would create a mold to recreate the missing piece with minimal seam showing. The red dye/coloring can come from any source(oil paint, etc.)just has to mix with the resin you selected and be translucent.
See some of my classified ads, I have some examples I recreated.
