If you added a Thing by accident or are no longer using removing it is quite simple.
A. Tap and hold on Thing icon. This will put all Things in edit mode and
reveal "X" in top right corner of each Thing icon.
B. Tapping on X will remove a Thing from your Thing Library
C. The Thing will automatically disappear from your Library. Tap "Done" and you will leave edit mode in your Library.
D. You can always add a Thing back to your Library at any time.
* Note: Before removing the Thing from your be sure it is not being used in any Flows.