With the release of 1.7, fixing problems in your cloud world is really easy!
You must be an admin to use this guide.
/repairin chat, this will put you into repair mode.
Click on a block, a red outline will be shown on the block
(Image credit: Everything that’s in 1.7 - MFS)
Click the block again, it will be restored to it’s original, generated, state. Any benches, chests, or shelves on the block will pop off as if you removed them with no inventory space.
Once you are done, type
/repairin chat to exit repair mode.
Important: There is no undo feature!! Once you repair a block, it is gone forever.