Adding a new project to a Jira issue
To add a new Balsamiq project to a particular Jira issue, you need to click on the "Add Balsamiq" menu option.
This will launch the Balsamiq editor, where you can create your wireframes (or import existing ones). This will also create a new Balsamiq Project file (.bmpr file extension) attached to your Jira issue containing all the resources that belong to a project (wireframes, symbols, images, icons).
If you do not see the menu option, please check with your Jira administrator that the Balsamiq for Jira app is installed and that you have editing permission on the current issue.