Go to Settings (in the PartFinder app)
Click the Add the PartFinder Widget Code button under Add Widget to Your Store.
Copy this PartFinder code to your clipboard
On your BigCommerce dashboard, go to Storefront > My Themes
Click on Edit HTML/CSS for the Current Theme
Click on Footer.html in the upper left
Note: we highly recommend you backup your template before making any changes
Paste your Part Finder code from the clipboard at the bottom of the Footer.html file contents and click Save
Add Widget to Your Blueprint Mobile Theme (If Enabled)
If you have a Blueprint theme and also have a separate mobile theme enabled, there is a separate step to add the widget to your mobile storefront.
Follow these instructions to customize your mobile theme: https://support.bigcommerce.com/articles/Public/Customizing-the-Bigcommerce-Mobile-Theme
You will want to add your PartFinder code to the Footer.html (which is found in the Panels folder).