Hi,
What kind of photos are you editing? I assume JPEGs? In this case all changes to these images are permanent if they have been saved and the session has been closed. Otherwise = if they have not been saved and closed yet, you can always used the undo function to revert the change (see screenshot - the arrow (1).
If you have just applied the label but not confirmed it via right-click yet, so that the border rectangle is still visible (see screenshot):
Then press 'Escape' on your keyboard would remove/cancel it as well.
In case you have accidentally saved and closed your changes on a JPEG, under certain circumstances, using the retouching function to clone out the label would still be possible. The more homogenous the background of the label is, the easier it is to clone it out. In the example screenshot, it would be very easy to clone out the 'Testlabel' by using the 'Image - Retouching - Clone destination' function, as the background is quite homogenously blue.
If you are however working with RAW files, then all changes are only applied to a copy. You can always access the original unaltered photo.
Hope this helps.
Cheers
Hoang-Tran