Add Search bar to menu

I just downloaded the plugin “add to search menu bar”. I was adding the padding and some other code, but when I tried to change the default text in the search bar, I couldn’t so I contacted the seller. They told me this: "It is disaplying by the Business Consulting theme that you are using on your site so you have to edit theme code by contacting your theme developer. "

What ca I do?

Thank you,