Changing Pinterest "Pin It" Button

I am trying to modify the Pin it button on the blog I help maintain, https://www.farmhousesoul.com. We want the pin it button that shows in the center when you hover over an image. I found the code on Pinterest’s website, but where to put in the code, I have no idea. I tried the index.php file inside the Nirvana’s theme folder but that didn’t work. Currently, we’re running the “Pin It” button via the Jetpack plugin and their “sharing” feature. Any ideas where I might put this piece of code?