Cannot add elements such as buttons to existing theme blocks

Hello, we are building a website using your theme here but we are running into an important limitation:Here we want to add a button below the headline but cannot find a way to do itSame here how can we add buttons below the 4 blocks of copy?We basically want to be able to choose any of the available elements on the theme and to add elements such as buttons to it. For example to take this block from the original theme , remove some elements such as the numbers and add others such as a button.