Hi there, swizzlee,
Thanks for visiting the Apple Support Communities. If we understand, you utilize a third-party device and its app to count steps. The steps are then synced from the app to the Health app on your iPhone, but you have noticed the data does not appear correctly. We are happy to help!
Based on what you've described, we suggest reviewing the information in the Apple Support articles Manage Health data on your iPhone, iPod touch, or Apple Watch - Apple Support and Automatically collect data in Health on iPhone - Apple Support.
If you are still having trouble with the data in the Health app after that, we recommend prioritizing the information from the KS Fit app in your Health app data sources. You can follow the steps below from the previously mentioned Manage Health data on your iPhone article above:
"Here's how to choose the sources that Health uses first:
- Open the Health app, then tap the Browse tab.
- Tap a category, then tap a subcategory.
- Scroll down, then tap Data Sources & Access.
- Tap Edit.
- Touch and hold the Change Order button  next to a data source, then drag it up or down in the list.Â
- To turn off a data source so that it doesn't contribute any more data for that category, tap the checkmark next to the source.
- Tap Done.
If multiple sources contribute the same data type, then the data source at the top will take priority over other sources. Any new apps or devices that you add go to the top of the list automatically, above your iPhone or iPod touch."
Should this not address your issue, don't hesitate to respond back.
Cheers.