The external system import link recently made available per The March 19th Release is not accesible from instances that are created with JIRA only.

To workaround for now, users will need to do one of the two below:

• From the Administration menu, use the keyboard shortcut g + g then type "External System Import".
• Access the URL directly via https://*YOURINSTANCE*.atlassian.net/secure/admin/views/ExternalImport1.jspa