Hi,
A cervical rib is an abnormality that's present from birth It's not usually a problem, but if it presses on nearby nerves and blood vessels, it can cause neck pain, numbness in the arm and other symptoms. This is known as thoracic outlet syndrome. Treatment would be Pain management and stretching exercises advised by Physiotherapist.
Next Steps
See an orthopaedic surgeon for better evaluation and then physiotherapist for assessment.