How do I log out of an account on Steam for Android?
Open the menu and go to Settings. Next to your name, there should be a big Sign Out button. Click that.
To log out of an account in Steam for Android, you need to bring up the menu on the left side of the screen (either by pressing 
or 
buttons) and then go to "Settings". At the top right of the "Settings" screen there is a "Sign Out" button;
Tapping sign out will log you out of the current Steam account.