Hello Hannah,
The "Diagrams" tab doesn't really require to create a new diagram, the main "white" area in that tab already is a diagram space, ready for use.
I took the liberty of looking into your review and found that you had a diagram saved, called "Review flow", to help you get started, I right clicked the first "Screening" codeset and picked the "insert child codes in diagram" option. This created 10 boxes in the diagram, one per each Include/Exclude code. I then moved the boxes around, clicked "Add counts" to include coding numbers within each box, and changed the colour of the "exclude" codes. I finished off by clicking "save" (saved as your only existing diagram "Review Flow", which was empty).
To see the result, you may go to the"diagrams" tab, click "load" and pick the only option you'll get. By default, the page shows a new empty diagram.
Overall, the diagramming functions of EPPI-Reviewer are a little cluncky, the way point-and-click works is a little confusing at first, but they still allow to generate flow diagrams to any desired level of detail. Also: the "coding numbers" get automatically updated each time you load the graph, so there is no need to collect and collate the numbers manually.
I hope this helps,
Sergio