Syncing app to my Apple Watch?

It would depend on if you allow the app to receive information from Health. There should be some setting in the app, and you would have to allow it in the Health app. Exactly how depends on the type of information you are trying to sync with the app.

I cannot see in the app description in the App Store if it uses information from the Health app on the iPhone or if it accepts info from the Watch. You may wish to ask the developer of the app.