I’m never sure about any app, but this sounds promising:
For many Tumblr users who’ve downloaded the app, it works. “I feel very safe using [Calm Harm],” says icantaffordadiary, who points to its cutesy interface as less intimidating than a professional-looking app. The Tumblr user tells The Verge that the app has been effective for reframing thought patterns. “There’s an activity that tells you to think of nice things people have said about you, and it helped me dissolve any negative feelings that I had towards myself,” they say. “This app helps people by giving them ways to take negative feelings and turn them into something good.”
Have you used Calm Harm to get through a period where you wanted to self-harm? Tell us about it.
Also, I saw this article at the same time, which mentions not only Calm Harm, but some other apps as well: