That something has been around a long time is no proof of, well, anything. You missed a chance to link us to a site with studies claiming with some degree of certainty the treatment works and is not just a result of a placebo effect.

https://sciencebasedmedicine.org/cupping-olympic-pseudoscience/

https://www.scientificamerican.com/article/can-cupping-treatments-raise-anything-but-welts-for-phelps-or-other-olympians/