Schema Premium plugin has support for schema.org HotTo type that allows you to add schema markups to How-To pages on your site.
Follow these steps to add the new markup type:
1- Create a new Schema markup
The very first step is to go to Schema > Types, and click on the Add New button.
2- Select schema.org HowTo Page
The next screen will open the quick schema.org creation wizard. Select the schema.org How To type from the drop down list.
When you are done selecting; Schema Premium will confirm the creation of the new schema.org type, and you will have the choice to go through next steps, which is configuring the schema.org type you’ve selected.
3- Configure schema.org HowTo
Create a set of rules to determine the target of this schema.org type.
For example, you can enable this markup on a specific page or post, or you may have a custom post type for How-To pages or a specific page that you would like to enable this type to work on.
3-C- HowTo Properties
Optionally; this section allows you to configure schema:HowTo properties.
4- Update Schema
Click on the Update button to update schema.org type.
5- Test Structured Data
Test your schema.org markup in Google’s Structured Data Testing Tool to make sure it’s valid. You can test your markup with a simple click.
Here is an article that explains how you can test your schema.