The extension has 8 samples for displaying the order product items. These files are located under

catalog/view/theme/default/template/extension/module/oc3/product_table_templates/

for OpenCart 2.3.0.2 or lower, the location is

catalog/view/theme/default/template/extension/module/oc2/product_table_templates/

To modify the template HTML,

1. Create a new file and name it, for example, custom_style_1.twig (custom_style_1.tpl for OpenCart 2.3.0.2 and lower versions)
2. Copy the code from any of the already available sample templates and paste it in your file
3. Make the required changes
4. Update the extension setting to locate this file location and save the settings