This is a vqmod extension. Therefore you need vqmod to be installed on your website. If you do not have vqmod, you can download this extension from OpenCart Marketplace https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=42736
- Extract the downloaded zip file, you will find order-list-customer-group-filter.vqmod.xml
- Go to Extensions > Modules > VQMOD Manager.
- Click on the upload button
- Choose this xml file “order-list-customer-group-filter.vqmod.xml“
- Your extension is installed, you can check your admin order list page