Link Issue
The "Link Issue" function will allow you to link existing project tasks with existing JIRA issues. This function is useful when you have tasks that have already been created in JIRA and/or are trying to repair a project plan that has been corrupted. You can also use this to build a complex project plan from issues that already exist by selecting tasks in Microsoft Project and linking them to their appropriate issue.
To use this function, select one and only one task from your project plan. If you select multiple tasks, you will receive a message that you can only select one task.
The "Link Task To Existing JIRA Issue" dialog will appear. Simply type in the JIRA issue you wish to link to or use the "Browse JIRA Issues" to select the issue and press the "Link" button. Your project task will then be linked to the specified JIRA issue.