Steps to accomplish:
Log into the your Shopify store with an account that has the permissions to edit the template files.
Open up your theme's template by:
Select Online store from sales channels.
Click themes from the submenu
Click on the 3 dots button:
Select Edit Code from the drop down menu.
Examine the theme.liquid file for any Facebook pixels.
You can quickly search large files by hitting Ctrl + f (windows) or Command + f (Mac). Searching for "fbevents.js" for a Facebook Pixel.
Remove any pixels you find.