Where to find specific H1 code in Maker theme for modification?

[onawave]

Hello - 

I have read many forums on changing the H1 heading to H2.

I understand how to do this as I've successfully done it with my "Add to Cart" text.

I'm specifically trying to locate this coding

"<h1 class="pn-notify-popup-heading">Notify me when available </h1>"

but cannot locate it in any of the code folders. Can someone point me to the right place/in the right direction to find this code in my Maker theme?

Thank you for any help/insight