I you hold a manicure certificate, you can set up an account with Sweet Squared to purchase the vast majority of CND products.
However they used to require you to take a conversion class to purchase Retention+ or Brisa enhancement products, to ensure techs learn the products' particular unique behaviours and techniques for use to get the best results. Not sure if that is still the case. Why not call to ask?
I personally think all techs should take a class when changing product brands to prevent common problems associated with not knowing how that brand works as a system compared to others. It's not about saying a previous qualification isn't good enough, but ensuring the science behind the particular brand is understood, and how it's particular usage may differ from what is required by other brands, for example why some brands require use of a primer, yet others are formulated not to need one.
Hope that helps x