MacKeeper is a scam notorious for leaving a huge swath of destruction in its wake.
Did you in fact download and install it? If so uninstall it forthwith. Follow its uninstallation instructions. They work. However, merely uninstalling it, even if you do so by following its instructions, does not undo the damage it and things like it are capable of inflicting.
... ,but seems unable to rid me of this ****** banner ,which shows a safari
mark in it .
It seems as though you are describing a Notification. Get rid of it by following these instructions: Stop unwanted Notifications - Apple Community. There is no need to download or install anything to fix that annoyance.
There are no viruses that affect macOS. Should you encounter anything stating the contrary it is an obvious attempt to defraud you. You may wish to familiarize yourself with Effective defenses against malware and other threats - Apple Community.