Report->Edit Selection Formula->Record
not({table.MyGroupField} in ["value1", "value2", <etc...])
Or you might create a multiple value parameter for the users to select, in which case the record selection would be:
not({table.MyGroupField} in {?MyParameter})
Successful posts tend to include technical information rather than vague descriptions:
Crystal version
Database/connectivity
Example data
Expected output
-k