Pretty easy 
Go to … Sign in
and log in. Choose the Tab “eLicensers” under these 3 big red buttons. Click on the right side on the show details triangle … scroll down to the end of the list of the elicensers content … there is a gray link “Remove USB eLicenser from Account” …
But … this is not possible for Software eLicensers. If it is an SeL … Steinberg Support must help.