This is a common misconception. Asexuals can still have a sex drive (arousal, desire for orgasm, etcc). The main difference is that they don’t feel a desire to achieve that with a partner. Asexuals might masturbate just for the feeling, without thinking sexy thoughts.
If you are looking to lower your sex drive, a sex therapist might be able to help. There are numbing creams, pelvic floor exercises, and certain medications that can reduce/help control sex drive.