What should I do if the old employees of the unit are rated as C?

First of all, find out if it's because of yourself. When the performance appraisal is C, the first thing to do is to communicate with the leaders of the appraisal in time, determine where you are not doing well, and discuss the performance indicators for the next year. If it's not your own fault, but the leader's score is unfair, then you can appeal or find the personnel department to understand the situation, and consider your own conditions, market environment and other factors to decide whether to find a new direction.