Hi,
the hidden actions indicated in the health check panel of the console are the one automatically generated when a computer is added to a manual computer group.
The only way to remove them is to use the external utility BES Audit Trail Cleaner that can be downloaded from the following link: https://www.ibm.com/developerworks/community/wikis/home?lang=en#!/wiki/Tivoli%20Endpoint%20Manager/page/Utilities
In particular you should refer to the tool options:
-g : Remove Hidden Manual Computer Group Actions.
-G : Hidden Manual Computer Group Actions expired over this many days will be deleted. (Default 180)
Regards
Francesco