A developer discovered that a product feature delivered in the last sprint would have greater business value with a small enhancement. What should the project manager do next?

The correct approach is to discuss the feature in the next sprint planning meeting. In Scrum, once a sprint begins, its scope is generally fixed to ensure focus and deliverability. New ideas or enhancements, even valuable ones, are typically added to the product backlog and prioritized for future sprints. Conducting another sprint planning meeting immediately would disrupt the current sprint and violate Scrum principles of stable sprints. Bringing it up during the retrospective is too late for planning and is meant for process improvement, not new feature introduction. Advising the team member to prepare the idea better before sprint planning is a good general practice but doesn't address the immediate next step for this specific valuable enhancement.