What to do if someone cuts their Finger off  It is surprisingly common for people to accidentally cut off part of their fingers, most often by shutting their hand in a slamming door or window or catching their fingers in a hinge or other moving part. If you know the most appropriate, immediate first aid treatment, you may be able to save the severed part and enable it to be re-attached. If part of a finger is amputated, the priority is to look after the casualty and keep them as calm as possible. Sit them down and try your best

Amputated, bruised and crushed fingers: What to do as seen on The Hippocratic Post.