Fluency is the ability to speak or write a particular foreign language easily and accurately or the ability to express oneself easily and articulately. I think if your level is between B2 and C1, you are already fluent in the language.
What do you want to improve in particular? Have a better flow in the conversation? Master grammar?
Thanks. You have a point. I didn't think it yet. I want to have a better flow in conversation, to be able to speak cleary and to build a high level of thinking. Do you have some advice to me?