Click the gear icon in the top-left corner of the data table and then click Reset, then click Yes in the confirmation window.
This will reset the table to the same settings that appeared when you first opened the assignment. If the assignment has some data or settings in the table, these will be reset to their original values when you reset them.
Note that this option will NOT appear to an instructor doing an assignment in Preview mode. It will only appear to students working on the assignment or when you are making a correct answer or a pre-populated table in the editor. To reset a data table in a preview, simply refresh the page.