You can get it if you google Samsung galaxy watch strava app, it’s about 4 or 5 down. It’s on my watch as I type this.
go to this on your phone
You don' t actually need the watch strava app anymore as Samsung Health now syncs heart rate data from a workout from the watch to Strava if you connect the Samsung Health app to Strava.
I have looked into this in depth and the Strava Watch app is not compatible with the Watch 3, so is not offered if you have a Watch 3 connected. I spoke to Strava who really didn't care less.