How to add button or call to action in the header

Can you post a link to the page in question?
It will then be easier to advise you on which method to use to place the widget (which hook to use) and which CSS is required.
(follow Rikards link above)

/* ==== Header widget area
Logo left, Menu right
Logo right, Menu Left
Logo center, Menu above
==== */
add_action( 'ava_after_main_menu', 'enfold_customization_header_widget_area' );
	function enfold_customization_header_widget_area() {
	dynamic_sidebar( 'header' );
}

/* ==== Header widget area ============
Logo left, menu below
==================================== */
add_action( 'ava_main_header', 'enfold_customization_header_widget_area' );
	function enfold_customization_header_widget_area() {
	dynamic_sidebar( 'header' );
}

after that create your new widget-area on :

_______________________

if you like to have the widget-area always nearby the logo – it might be better to use a filter to place the widget area:
See here a different solution with a widget area inside logo container ;)
https://basis.webers-testseite.de/
tell me – if this is what you like to have – and if your header setting is in this way.

See snippets and basic css for that on: https://webers-testseite.de/fiorettipau/

i inserted to that widget-area a html widget – (copy&pasted html code from an enfold button-row)
Of course, you have to adapt the CSS to your header configuration. And you may also need to set a responsive behaviour.

f.e. if you got a shrinking header – you had to decide f.e. if you set the widgettitle to display none on header-scrolled.