Go to your event menu, select Communications and scroll down to Waitlist Email Settings.

First select the template you'd like to use for the email people on the waitlist will receive if they are invited to register if a place becomes available. If it's not a pre-populated template, add your content.

Set the notification email address that will receive notice of new people joining the waitlist.

Then select the email template you'd like to use for the email people joining the waitlist will receive. If it's not a pre-populated template, add your content.

Once you're done, click Save Settings.