You would need a script in Workflow. That script could lookup values in a database and then add these values to each line of the CSV, based on a unique ID. Note that this solution is very unlikely to be the best one, but your question just doesn’t have enough information for me to provide alternatives. Using metadata to complement your original CSV records would probably make things much easier, but again, this is pure speculation at this stage.
Also, note that when asking questions in this forum, you should not only type the question but also fill out the “More information” field. The more info you provide, the more precise (and the faster) the responses will be.