Which header style are you using? All header elements can be edited out by just clicking on the element, then the elements options will unfold in the left sidebar. make the changes you need there. Or in case of just text, click on the text to start editing it.
Can i please see a link where are you running this? So i can understand better the situation.
Sorry this is not possible. You can add only the elements listed in the Codeless Builder > Add element (screenshot).
Or you can try with a custom membership plugin.
