All the format attributes of every element in a table have a "default" setting. These are established using the Preferences and Default Formats. Each attribute can be changed through certain entries in the Format (Table Part) dialog. To return any element to its "default" state, i.e., return to all the default settings in the dialog, just click on the Reset button at the bottom of the dialog.

Note: There is NO "undo" for this operation. All custom entries are lost.