How to fix my knee in a brace for basketball?

Depends. It is hard to answer this question if we don't know why you are wearing the brace in the first place. Are you wearing it for a ligament injury, prevention, tendonitis or just because you think it gives you support? I am not a big fan of knee braces if you are using it with the thought it gives me more support. A regular knee sleeve is going to give some compression, not support.
Have it evaluated. Different knee conditions may need different types of supportive braces. Have your knee evaluated by a professional and get the appropriate type of brace for your condition.