This may seem trivial, but there's no way to reset it, and no doc that mentions it. There are a couple of posts on this board, but the answer seems to have gone astray - please tell us.
Hi - the default shortcut was cmd-opt-shift-] ... but the reason there is no reset button or particular documentation about it is I don't feel there is a strong reason to use that shortcut. You should use whatever shortcut you like.