Hello, I was having the same issue. Here is what I did.
You first need to add the My Templates app to your Outlook. In a new message, Insert>Apps>Add Apps> search for My Template
The following is from the Help tab in Outlook, I searched "Template":
Create or edit email templates
In the new Outlook for Windows, templates are similar to quick parts in classic Outlook. They are text-only; no graphics or formatting included. But they can contain multiple paragraphs.
- In a message you're composing, on the Insert tab, select
Apps > My Templates. (The first time you use My Templates, click through a description of the feature to get to step 2.) - To create a new template, click
Template, then give the template a name and enter the text you want to include. - To edit an existing template, point at the template name, then select
Edit template.
Tip: For info on how to use the new template, see Open or use an email template.
I hope this helps.