On iTunes at itunes.apple.com
Some self help apps (like books and courses) have dubious records. It seems that they work for some and not for others. If you suffer from anxiety or have trouble managing your stress, then it is possible that an app as simple as iStress may help you. They use several techniques, one of which may work for you. The thought reframing is an old concept that has some merit, and the app may help you keep at it enough to experience a little success at managing your stress.