Understand the Metric:

The first step is to get a clear understanding of how the rider rating is calculated. What factors influence it? Are all riders experiencing the same drop or are there specific segments that are more affected?

Identify Timing and Pattern of the Drop:

Is the drop sudden or gradual? If it's sudden, it might be related to a recent change in the product, a system error, or an external event. If it's gradual, it could be due to a longer-term issue like deteriorating service quality or increased competition.

Investigate Internal Factors:

• Product changes: Were there any recent updates to the app or changes in the way drivers are assigned, routes are calculated, or how ratings are captured? Have these changes been communicated effectively to the riders?
• Service Quality: Could the drop be due to issues with the drivers or the bikes? It could be useful to segment the data by driver, area, and type of bike to identify any patterns.
• Technical issues: Are there any bugs, crashes, or performance issues in the app that could be affecting the rider's experience and hence the rating?

Assess External Factors:

• Competitive Landscape: Have there been changes in the competitive landscape, such as new players, aggressive marketing from competitors, or changes in their rating systems?
• Regulatory or Legal Changes: Have there been any recent regulatory changes that could be impacting the service or its perception?
• Societal Events: Could social, economic, or environmental events be influencing rider sentiment?

Evaluate Related Metrics:

Are there changes in other related metrics like rider complaints, number of rides, average ride duration, etc., that could provide clues to the rating drop?

Engage with Stakeholders:

Speak to customer service to understand if there have been increased complaints. Interact with drivers to see if they've observed any changes.

User Research:

It could be valuable to directly reach out to riders to understand their experiences and their rating behavior. Surveys, interviews, or focus groups could be tools for this.

Once I've gathered all the necessary information and identified the likely root cause(s), I would devise a strategy and action plan. This could range from technical fixes, improving rider-driver communication, enhancing driver training, refining the rating system, or running marketing campaigns.

The key is to monitor the metrics closely after implementing changes to ensure that the rating improves and to continue iterating on the strategy until the issue is fully resolved. Remember to communicate with all stakeholders throughout this process to ensure everyone is aligned on the problem, the proposed solutions, and the expected outcomes.