Hi there AnnaG89,
Have you tried adding the data from this specific app to the Health app with these steps:
Add information from other apps
1. Open the Health app.
2. Tap your profile picture in the top right-hand corner .
3. Under Privacy, tap Apps. You can see apps that you already own that are compatible with Health. If you can't see an app, it may not be compatible.
4. Tap an app and turn on the health categories you want that app to track.
You may also need to open the app and adjust its settings to allow it to share data with Health.
If you don't see the app listed, as you mentioned, it may not be compatible. If it's not compatible, you can add the information manually with these steps:
Enter information about your health
1. Open the Health app and tap the Browse tab.
2. Tap a category, such as Activity.
3. Tap a subcategory, such as Steps.
4. Tap Add Data in the top right-hand corner.
5. Enter the date, time and data for that activity.
6. When you've finished, tap Add.
You'll find these steps and more information here: Manage Health data on your iPhone, iPod touch, or Apple Watch - Apple Support
Take care.