If enabled globally and you were granted permissions to browse the app, you will be able to see the Calendar tab in the issue Activity section. It displays the other issues of the project assigned to the current issue assignee, in case their start and end dates are specified (the issues are planned).
This section may help you to understand the assignee's workload. Select the period to plan the current issue. Here you can also re-plan the existing issues using drag-and-drop.