1. In requirements tab select coverage view
2. Select requirement by clicking on parent/child or grandchild
3. On right hand side(In coverage view window) another window will appear. It has two tabs
a) Tests coverage
Test coverage tab will be selected by default or you click on it.
4. Click on select tests button a new window will appear on right hand side and you will see a list of all tests. You cans elect any test case you want to map with your requirements.