relaxation rteduces OCD
OCD, obsessive compulsive disorder is classed in the diagnostic manual used by psychiatrists, as an anxiety disorder. There are many other more serious mental disorders, but OCD is just from anxiety.
at the risk of stating the obvious, anything that relaxes you will reduce your stress and anxiety and therefore must reduce your OCD, also anything that relaxes your body will also relax your mind
for relaxing your body, massage is excellent although it can be expensive, home massage books are available and it can help a lot if you can get a friend or partner to massage you
jacuzzi or spa baths are very relaxing, but can tickle until you get used to tem, hot tubs or simply a long soak in a hot bath also helps, in japan, everyone has long soaks in a very hot bath for relaxation
more exercise done in a gentle way is relaxing, especially long walks, maybe join a gym