Apple Watch and Garmin HRM Pro Plus

Is it possible to make the Garmin HRM the default monitor rather than the watch? When going for a run, I use the watch to manage my run, I often use the run plan function to create repeating sprints or tempos. All runs are then saved in Strava. I'd like to continue using the watch but take HR data from the Garmin when I wear it. I don't wear the Garmin for functional strength training, only running so would like to make the choice of item fairly easy to alter, better still, the Garmin is the default and when not detected data reverts back to the watch HR function.

Any help is really appreciated, I've asked Garmin support but they can't help.

Thanks.