Please go to either the Diary or the Progress tab on the bottom of the app,  then tap on the Profile icon in the top right corner and then on the gear symbol in the same location. Your Settings are here.

If you scroll down to the end of the list you will see the button Log out.

Reset:

In your Settings choose Account Settings. At the bottom of the page you will find the Reset data button. Clicking this button will erase all tracked data but will save any item created under Favorites (recipes, meals, food, trainings).

Note: This action cannot be reversed.