There are several ways to begin using the add-on. If you start the visualization from the Jira search screen, it will be pre-populated with your search criteria.
You can start the process using the Visualize issues link in the Issues menu.
Project tab panels
You can also find the Visualizer in Jira project tab panels.
In the Jira search screen, click the Export button and then Visualize. This action will start the visualization using your search criteria.
Due to a limitation of Jira itself, the Export action will produce an error when the query exceeds 300 issues.