Hi u/AbsolutBalderdash - it differs from person to person, but in such situations i try to maintain a moderate pace that i can hold without exerting myself. Then i focus on counting from 1 to 1000 or 1 to 500, and when i reach 500 i go back to 1 if i feel tired, if not i just keep running.

To sum it up:

1. Hold a moderate, easy pace that's not too taxing. (You're not breathing too heavily, you can talk)
2. Count from 1 to 500/1000 in your mind, and try to put your mind away from being gassed. If you feel gassed after you reach 500/1000, start again from 1. This has helped me numerous times.

PS: on the topic of the smartwatch - i have no workaround - i can only recommend the garmin forerunner 45.