How do I change default volume on S8 (7.0) alarm?

[Android Central Question]

I really like the tune of the default alarm on my S8 running android 7.0. But when I try to change the volume (clock - alarm tone and volume) it makes me choose from 32 tunes....none of which is the default tune. How can I change the volume of the default tune? (I don't know what this tune is called, because as stated above, it does not come up on my list of tunes. I've tried each of the 32 tunes, but none is the "default" tune).