The best approach for the agile coach would be to address the root cause of the concern immediately and help the team reflect on their current processes to identify ways to improve. This can be achieved by engaging the team in a discussion that focuses on understanding the issues related to the technical design and the definition of done (DoD).
This will allow the team to openly discuss and identify specific areas of the technical designs that do not meet the DoD. By understanding the underlying issues, the coach can help the team find solutions and ensure that future work aligns with the agreed-upon quality standards and expectations.