How do I start a career in career counselling?

In short three lines, I can say about it

1. Know what you need to do professionally as a career counsellor
2. Develop the knowledge, skills and abilities in necessary processes, tools, procedures etc.
3. Learn how to ensure the outcome to the clients.

Some professional career counselling certification programs like C5 or CICCP from reputed schools like ISCHS can also help you to be a professional career counsellor and start your profession. However, there are plenty more options too depending on your purpose of becoming a career counsellor. All the best