At first, the Reminder application should be added to your Jira and enabled. Read how to find, add and manage the Server apps (Atlassian documentation).
After installation, the Reminders section will appear in the Administration → Manage Apps menu, Teamlead section. Also, the My Reminders section will be available in a user Profile drop-down menu (check the User Guide).
Use the standard Jira hotkey g+g to reach the Reminders settings from any place in Jira: