Transfer a screenshot from the watch to my phone

[CamFlyerCH]

I own a Watch 4 Classic and screenshots are transfered to my phone instanntly after I take one. But if my phone is not reachable (during sports) the screenshots are only available on the watch. I could not find a way to transfer them later to the phone. 
I found this description: https://www.samsung.com/sg/support/mobile-devices/how-can-i-take-a-screenshot-on-my-galaxy-watch/ 
But if I long-press a picture in the gallery app, I can only delete it or use it as a watchface background:

So how I can transfer the missing screenshots to my phone ?

[CamFlyerCH]

For example the screen during pool swimming to discuss and explain the shown data to a friend.

[realaud]

Oh, ok. But those stats are also delineated in the app.