First of all - you don't need to install EclEmma if you're using one of the following Eclipse Oxygen 4.7 packages - Eclipse IDE for Java Developers, Eclipse IDE for Java EE Developers, or Eclipse IDE for Eclipse Committer, because EclEmma is now part of these packages.
So how exactly you installed it? And please provide us content of Help -> About Eclipse -> Installation Details -> Configuration , and Eclipse log file located in your workspace under .metadata/.log
Can you try fresh installation of one of the mentioned above Eclipse Oxygen packages?
Please make sure that you're in Java perspective to see the icon in the toolbar. If you're talking about main menu, then also please make sure to be in Java perspective. Or/and check presence of "coverage" context menu by righ-clicking on runnable Java resource, e.g. unit test.