Add Mobile "back to top" button

That really depends upon your theme. What theme are you using? Where did you download it from?

The theme is a custom theme, Flatsome – It was downloaded prior to my taking the site over

https://www.chicagometalsupply.com/homepage

I’m sorry but as you appear to be using a commercial theme, you need to seek support from the theme’s developer/vendor. We do not have access to, nor do we support, commercial products here. Try https://themeforest.net/item/flatsome-responsive-woocommerce-theme/5484319/support