How to add button in the Header?
Header Button
From your WordPress Dashboard, go to Appearance > Customize > Header > Header Button section.
Add your text in the Button Text field.
Insert the link in the Button Link field to redirect the button to the link.
Click on Publish.
Note: You need to have an assigned Primary Menu to display the header button.
It is shown in the image below:

If you need another header button, it is available in Pro: Header Button Two Overview (Pro)
Updated on: 24/08/2022
Thank you!