How do you handle a problem that a co worker created downstream?

When addressing a problem created by a coworker downstream, I first ensure I understand the issue thoroughly by gathering all relevant information. Then, I approach the coworker privately to discuss the problem constructively, focusing on the impact rather than placing blame. Together, we brainstorm potential solutions and agree on a plan to rectify the situation. Finally, I communicate with any affected parties to keep them informed and ensure transparency.