You can create the defect at the time execution and associate the same to Test Scenario/Action steps/Step units. Also, you can associate the existing defects to Test Scenario/Action steps/Step units.
Go to execution screen > click on 'add defect' icon.
A: You can search for existing Bug/Defect searching with summary or JIRA issue ID.
B: You can add new Bug.
Here is the link to help documentation.