In this guide, we will show you how to add header and footer on One Step Checkout extension.
Firstly,you need open file onestepcheckout_index_index.xml at path
with any editor. On this guide, we use Sublime Text to edit.
After you open file complete, please following on this screenshot.
After editing the file, you should save and flush cache on Magento and go to One Step Checkout page to check it.