To access DESelect Segment log in to Salesforce Marketing Cloud.
On the menu bar on top, over the AppExchange icon and then click DESelect Segment.
Within a few seconds, the DESelect Segment overview page should be loaded.
In case you don't see DESelect under the AppExchange menu, ask your SFMC administrator to grand you access.
If you need support in this, please reach out to your Customer Success Manager at DESelect.