The 'Odoo Helpdesk Walkthrough, for customer service teams' YouTube video (https://www.youtube.com/watch?v=5JSIOYLcWU4) and 'Odoo Helpdesk: A new application for customer service teams' page (https://www.odoo.com/event/odoo-experience-2016-2016-10-03-2016-10-07-420/track/odoo-helpdesk-a-new-application-for-customer-service-teams-481) refer to a 'Canned' Responses feature. This feature is also mentioned on the Helpdesk | Odoo webpage (https://www.odoo.com/page/helpdesk).
Access to this feature is missing from the Helpdesk Team configuration page. We are using the Online version of Odoo 10.saas~14+e (Enterprise Edition).
Is this feature no longer available?
There are three SAAS versions of Odoo 10 above the one you are using (15, 16 and 17) - I am willing to bet the video was made with a later version.