"How do I report 1120-S K-1 income as self-employment income?"

You simply cannot report K-1 (1120-S) income as self-employment income. 

Shareholders of an S corporation are not self-employed; they are employees of the corporation if they perform services for the corporation on a regular and continuous basis.

If you did not pay yourself a reasonable salary, you might want to consult, in person, with a tax professional.