Final answer:
Offering to help the coworker resolve the customer issue is a constructive approach. Engaging in open and honest communication and focusing on problem-solving fosters a healthy work environment, and if necessary, they should go to HR or a supervisor for further assistance.
Step-by-step explanation:
If a coworker frequently complains about a problem with a customer, rather than ignoring their complaints, telling them to stop complaining, or reporting them to the supervisor, offering to help resolve the issue is usually the best course of action. This approach embodies professionalism and problem-solving skills. Initiating open and respectful communication by asking open-ended questions can provide more insight into the coworker's perspective. Acknowledging what the coworker says and confirming your understanding can have an affirming effect. Focusing on problem-solving instead of assigning blame helps to maintain a positive work environment and could lead to a quick resolution. If a coworker's complaints persist and you're unable to assist, recommending that they speak with a supervisor or the HR department could be the next step.