Neuronal plasticity is the brain's ability to change its connections in response to learning, experience and injury, throughout life and especially in childhood.
Every time you learn a skill, the connections between the nerve cells involved change. That is plasticity. It is how practice works, and it is part of how people recover some function after a stroke or brain injury.
It does not mean ADHD or autism can be trained away. Both are neurodevelopmental. They describe how a brain developed, and that stays part of who you are. What plasticity does mean is that skills, routines and strategies can be learnt at any age.
Be cautious of products that promise to 'rewire' an ADHD brain. That is a marketing word, not a clinical one.