One of the many uses of a reflector in photography is to help eliminate dark circles around or under the subject’s eyes. To a certain extent it can also hide or at least diminish eyebags.
My daughter Maia sometimes has dark areas under her eyes early in the morning. But then early morning is also the best time to take pictures inside our house, because of the sunlight coming in through the large windows facing the east. In the photo above, the sunlight is the hairlight, and the reflector catches that sunlight and bounces it back to her face and creates a catchlight in her eyes as well.
It may take a few adjustments of how the reflector is positioned or held before you can get the best light possible. And when you do, it’s time to snap.