You can follow the step-by-step guide below to duplicate a template.
How to duplicate a template:
Step 1: Go to Design Manager and open the site you would like to add new templates to.
Step 2: Go to the “Actions” drop down and select “Add Template”
Step 3: In the “Add Template” dialog, click on “Percussion Templates” radio button and in the dropdown that says “Base” navigate to the site that you would like to copy templates from.
Step 4: Choose the template you would like to duplicate and click Save. You should see the template appear in your Design Manager.