There are two ways to stop following a user or Chef:
The first one is:
Access the person's profile;
Click on the "Following" button, just below their username;
Confirm the action in the pop-up that will appear.
In addition, you can also stop following people by accessing their follower list. To do so:
Access your Profile from the bottom bar of the app;
Under their username, tap "Following";
Next to the users name, you can press the "Stop following" button;
A pop-up will appear for you to confirm the action.
That's it :)