For iOS users currently using Trainerize there's no need to download anything new—your app should dynamically update to Viking fitness branding shortly. (If this doesn't happen within 24 hours, try logging out and back in again.)
Note that the new version of the Viking fitness app requires that your device is running on iOS 10.3 or higher. You may also need to upgrade your Trainerize Fitness App to version 5.0.0 or higher.
If you are a new iOS user or want to install your custom app on a different iOS device, head to the Apple App store and download the Trainerize Fitness App. The branding for Viking fitness will appear after you login for the first time.