The Benchmark represents a group of audits or assessments that you want to compare your results to. By default any industry groups identified in your audit or assessment are listed as possible comparison options at the top of the selected audit page (see 1 in the image below). 

The selected Benchmark is highlighted (see 2 in the image above). You can change the Benchmark for Comparison by clicking on any other listed default benchmark.

If you want to compare your results to a different industry group click on Add Industry (see 3 above) and select the required industry from the dropdown. This will add the selected industry group to add to the available possible comparison options (see 1 above).