Trouble adding a link to the header image.

Because Sela uses a background image for the custom header it’s not really possible to add a link to that area in the traditional way.

Instead of using a custom header, I’d suggest you try Sela’s Site Logo option, which is available after activating the Jetpack plugin on your site. You’ll see the option to upload a logo in your Customizer, in the Site Title, Tagline, and Logo section. If you upload your image this way not only will it be clickable, but it will adjust to smaller screen sizes automatically, which the background image/custom header does not.