All data used by Weight Only is totally controlled by the user. If the user has a device with Health Kit available and it is enabled, the data is stored there. If the app is deleted, the user has the option to retain the data in Health Kit or delete it. That function is provided by iOS. If Health Kit is not used, data is stored with the app. Any data gathered this way is deleted when the app is deleted and cannot be restored. No data of any kind is collected or sent to third parties.
If you need support you can contact the support team by email.
When running the app for the first time, the app will ask to access and update Health data. If you grant permission to write weight information, data entered in the app will be saved to Health Kit. If you grant permission to read weight information, data already in Health Kit will be available for display. If you don't grant these accesses, you can still use the app, but data is not saved in Health Kit but stored with the app. If you then delete the app, that data will be lost.
After granting or denying permission to Health data, you are presented with a brief instruction sheet. This is displayed only once. To see it again, you would need to delete the app and install it again.
To use the app, simply enter a weight in the provided field. Press DONE to enter it alone. Press NOTE to include a note with the weight entry. Upon entering the data, the graph will be updated.
If you have enabled Health Kit, you may enter historical data there. The app currently has no way to enter historical data.