The following are requirements and recommendations to install a Garmin Running App from the Connect IQ Store

Ensure you have the necessary Garmin devices to support running power, as described here.
There are several Garmin running power apps available. Try the basic one first that simply shows your current running power. The other apps enable you to view related metrics like lap running power, last lap running power, or average running power. See a description of the different apps here.
Once you’ve downloaded your running power app(s) to your watch, you need to add the running power data field to your data screens. This is done in the watch menu under Run Settings > Data Screens.