@moreusernameftw
First you need to pair the Verity Sense to the watch. You can do this now, no need to wait until you’re ready to run/exercise.
To pair the VS sensor, put it on your arm and turn it on. Then go through the settings/connectivity/pair sensor menus on your watch and select “pair HR sensor”. It’ll tell you to moisten the sensor, which you can obviously ignore for an optical sensor and click to the next step. The watch will then search for and pair to the sensor within a few seconds.
When you want to run or whatever exercise using the VS sensor, put it on, turn it on and then go to the exercise start menu in the watch. The watch will automatically connect to the VS, overriding the watch wrist sensor (no need to disable it). As above, you’ll know it’s connected because the heart symbol will have the little “wings” (belt). If you’re still not sure if it’s connected to the VS before you start running, take the watch off and check that the wrist sensor lights are off.