Could you please mention the link of your site also, so that it will be easy to both of us to find the solution asap. But if you have kept the header image as background image then please remove it and please follow the following steps:
Go to Dashboard => Appearance => Widgets => Banner => Keep the text widget inside the banner widget and keep the image like this
=> Then save it
We hope this will be helpful to you, if not then please let us know.