If we understood how learning or the brain worked, maybe we'd understand how neurofeedback works. https://eeginfo.com/what-is-neurofeedback.jsp In short though, what we believe is happening is an exercise of the timing and coordination of brain circuits. We aren't fixing anything, we're just showing the brain its own timing, and the brain does more with that than we understand.

Neurofeedback, also known as EEG biofeedback, neurotherapy or brain training,  is a learning strategy that enables people to alter their brain waves and exercise the brain's own regulatory mechanisms. It is used for many conditions and disabilities in which the brain is not functioning as well as it might.​

Research has demonstrated that various EEG (brainwave) frequencies are related to specific qualities of arousal, attention, mood and consciousness. Particular patterns of these frequencies determine the difference between peak performance and malfunction, between getting A's and failure, and sometimes between joy and despair.

Neurofeedback is a safe, painless and noninvasive method for teaching the brain how to better regulate itself. When information is "fed-back" to the brain visually and by sounds, the brain can optimize it's own activation level and its focus, attention and mood.

Neurofeedback is used as an aid for optimal brain functioning, for people interested in Peak Performance and people seeking treatment for problem conditions and injury. These include Attention Deficit / Hyperactivity Disorder, severe conduct problems, specific learning disabilities, issues such as sleep problems, teeth grinding, chronic pain, headaches and stomach pain. It is also helpful with mood disorders, anxiety, depression, substance abuse, weight control, seizures, and secondary stroke symptoms. (https://www.brainfitnesscentre.com/neurofeedback).