@Meneillos sorry but i don’t get it.
Your S5P is connected/linked with your Android phone, right?
Then you need to link, your external HR band with your S5P
https://www.suunto.com/Support/Product-support/suunto_5_peak/suunto_5_peak/features/pairing-pods-and-sensors/
Finally, every tiene you want to record an activity, wear the HR band, and press Exercise -> Run (or any other activity type) and wait for GPS and HR band.
I have never had a problem with that
I hope this helps