How can I sync data from Samsung Health to Exist?

Exist doesn't integrate with Samsung Health directly, but you can sync your Samsung Health data to Health Connect, and from there sync it to Exist.

Once your data is in Health Connect, you can set up Exist to sync from Health Connect inside the Exist for Android app. Open the app, tap the "cog" icon to get to Settings, then tap "Health Connect attributes" menu item. Turn on the necessary settings to sync the data you'd like to come from Samsung Health.