The easiest way to download the TELUS Health Companion app is to download it to your iPhone first, as by default, apps on your iPhone that have a watchOS app available are automatically installed and appear on the Home Screen.
To download the TELUS Health Companion app on your iPhone, go to the App Store and search for TELUS Health Companion, then download to your phone. The corresponding Apple Watch app will also install on the watch. If you do not see the corresponding TELUS Health Companion app on your Apple Watch, check that the latest Apple Watch O/S is installed.