You will need to long press the screen of the Apple Watch Stryd App for the Run Control Screen to appear in order to end or pause the run. Once you long press the screen, you will be presented with options on how to finish or pause the run.

Alternatively, after updating to v7.3.2 or later, If you are unable to long press the screen, you can scroll to the top of the screen for the Run Control Screen to appear to finish or pause the run.