1. Log into the CMS of your portal:
2. Under 'Quicklinks' in the middle of the page, select 'Sitebuilder'
> 09 (this directory could be a different number, or there could be multiple ones, as the naming convention is based on month)
This is the directory where the messages get laid down as .xml files. Find the one you are looking to clear/delete and hit the red 'x' button on the xml file
The message will no longer be displayed on the dashboard of API Portal.