First, just select the row or rows you want to use as the repeating header, (don't select the whole table).
Quick select a row - cursor outside table on left hand side opposite required row then left click mouse.
Now right click to get Table properties and check the 'repeat as header ...' check box.
You may have the 'repeat as header ...' check box checked for the whole table, if so you will have to clear this before selecting a single row, so select whole table, then table properties and clear the check box. Then select the row as described above.
Hope this helps