The initial page you see when you install the DMM component from the OutSystems Forge is the Dashboard:
To access DMM, press the center top area where it says "Go to Data Migration Manager".
When you publish the DMM component it will automatically run an analysis on your OutSystems database to present it to you on this dashboard, has shown above. This analysis may take a few minutes, so if you access the component right after publishing, it is normal if there is still no data available to show.
If you want to rerun the analysis, or set another frequency or configuration for it, you can do it in the Service Center in the Timers tab: