how can i change challenge setting

how can i change challenge setting
i can't even find 'My Settings' >> 'My Challenge Settings' menu.

Click on your own icon avatar/pic at the top right of your screen. [In your case it's a big yellow button.] My Settings is at the bottom of the drop-down menu.

In the app: click at the top left and go down the menue, near to the bottom you find "My settings"