First, turn on advanced mode:
Dunno why they had to put this behind an unlabeled 'secret' button...
Open the properties pane but clicking on View > Properties.
When you turn on 'advanced' mode, the 'Row Groups' area will get a whole bunch of new items. Click on them one at a time and find the one that you want to repeat. Often it is more than one, but let's just do one for now.
In my report, I wanted the first row to repeat. When I clicked on the first 'static', I got the highlighted cell that you see in the top left corner of the report. Set the properties for that 'static' like you see below, and it will repeat.
Woot!