Note that clicking on another template will result in losing the edits made in the existing template. It is strongly advised to export the customized template immediately after making the changes to avoid any rework.
Refer Import/Export to export the customized template.
Steps to do custom editing on predefined template
Navigate to the “Template” option in the top ribbon.
Image 2: Template option in ribbon
Hover over the Template and Click on the "Marker" icon located at the top-right corner of the template.