One question deserves another. Are you wanting to open an independent stand alone fit studio, a fit studio in a bike shop, or an adjunct to another related business (coaching, PT, other?) What fitting experience do you already have? You'll need customers, tools, skills, experience, and yes - probably some credentials / certifications. One workshop or certification does not make a bike fitter, but it does kick off a long journey of learning and gaining experience. Do you live in the USA or elsewhere? That will influence what courses are reasonably available and accessible.
John http://fitkitsystems.com http://www.bikefitr.com