How to adjust text in plugin

Hi There,

I’m having trouble with the plugin : https://wordpress.org/plugins/background-manager/screenshots/

This plugin has a ‘+’ sign that shows a title and text thats added to a picture. As can be seen here: maestro-uitvaarders.nl

The only thing I want to do is adjust the ‘+’ sign to a personalized text. Anybody that knows how to help me? Would mean allot to the owner.

Thanks