To modify the theme, you have to open the customize page. If you don't know how to do that, please refer to here.
Our theme has provided the google maps in the contact section which is shown at the contact page.
You can edit the contact section in Customize, choose the contact page, then click "Contact Us" section on the left. Note: the contact page should be created in Online Store > Pages and must have the template is "page.contact".