You can only apply for the Innovator visa if you have received endorsement for a new business idea or have previously received endorsement for an existing business for a Tier 1 (Entrepreneur), Start-up or Innovator visa.
If you are applying for endorsement based on a new business idea, you must be a founder of the business.
You are not able to apply for the Innovator visa to join an existing business in the UK which is already trading.