How can I edit the 'how heard of us' checkout popup in my store?

[katie_leary_seb]

Hi -

A while back I created a pop-up for my store (theme - Supply) that asks buyers where they heard of us & allows them to input notes pertaining to their order. I need to edit it but for the life of me cannot remember how/where I added this so don’t know where to find it to edit.

Can someone please help me locate this so I can make necessary changes? I did a search on how to set a popup at checkout thinking that would remind me & it said to add a snippet but I looked and I don't have one so that's now I did it. 

Any thoughts on where or how to find this are greatly appreciated.