You can only connect data sources in Welltory Premium. You can sync all MiBand data with the Welltory app.
Please note that some Mi Band devices measure heart rate variability but do not transfer this data to other apps due to the developers’ policy.
If you have an iPhone
Download and install Zepp Life (formerly MiFit)
Open Apple Health and go to Sources
Select Zepp Life and turn all categories on
If you have an Android
All done! Welltory should be getting your Zepp Life data.
Note! Synchronization takes time. That's why the data can't instantly appear on the graphs right after syncing. Sometimes it can take a few hours or one day. For example, if you analyze sleep, the data won't be uploaded on the graph right after the night but the next day.