Did you search the forum first? This topic has come up several times before, but I’m not sure what you want to link to.
By default, the header image links to the home page.
The header image does not have a link on the home page, since you are already in the place where it would take you. Thus clicking on it would force an unnecessary page refresh.
If you want it to link to something else, here is a thread from two weeks ago: