Heartbeat Data Collection App Development

I'm in need of a skilled app developer with experience in obtaining raw heartbeat data from Apple Watch.
I already have a functioning MVP that needs some updates.

Key Responsibilities:
- Develop an app that collects heartbeat data (inter-beat intervals, R-R, or P-P intervals) for research purposes. This is not the processed "heart rate" or "SDNN" or "HRV", but specifically the raw beat timing data.
- Update my currently functioning app to include this new data
- Ensure the app sends data to Firestore seamlessly.
- Apply basic web design skills to create a very simple interface to download the data.

Skills:
- Proficiency in Apple Watch app development.
- Already knows how to obtain raw beat timing data
- Apple HealthKit experience
- Experience with Firestore and cloud data management.
- Basic web design skills
- Fluent in English
- Understanding of health monitoring and fitness tracking data

Your bid should reflect your experience with similar projects and your ability to deliver an app that meets these requirements.
The successful bidder should be able to demonstrate/explain/assure me that they know how to obtain the kind of data that I am looking for.