Harmless is an organisation who work to address and overcome issues related to self-harm and suicide. They have a range of resources aimed at helping people understand self harm and how to support a loved one who is self harming.
The Youngminds website includes advice and information for parents about self harm including: reasons for self harm, common myths, and how to support a child who is self harming.
Calm harm is a free app providing support and strategies to help you resist or manage the urge to self-harm. Download from Google Play or App Store.