How do I cancel an activity

I fell asleep wearing my apple watch. Sometime during the night, I activated a fitness application that also started an activity.

I know how to dig through the app and delete that data.

HOWEVER

Calories and other amounts will remain embedded within else where in the app. Therefore showing inflated activity.

SO HOW DO I

when I notice the rogue activity how do I cancel it so I don’t have to do surgery within the app to get rid of its data.