Voiding retailers in Inzant Sales is only possible from the Management Portal / Web Client. You'll need Admin user privileges to be able to login and perform edits of this nature.
Once logged in, navigate to the retailer search screen. Click the "Retailers" icon in the top menu, then in the retailer widget click the top heading zone to open the search screen.
Once the search screen is open double click on the retailer from the list to open the details screen. If the retailer list is quite long you can cycle through the pages to find the retailer, or better yet simply do a search to find the retailer quickly.
Once you've opened the details screen, to void the retailer click the red trash can icon in the top right of the screen.
You'll be prompted to confirm the voiding/deletion, click OK to proceed and void the retailer. Its important to note that this isn't a permanent deletion, you can always reverse this operation should you need to reactivate the retailer for any reason - see a quick guide on reactivating a retailer here.
After voiding the retailer you should be returned to the retailer search screen. All done!