Fix blog logo link

We have a main website www.example.com and then the blog is on a sub folder www.example.com/blog/ , we have a logo on top of the blog site, that needs to be linked to the main website. Already tried using various plugin's and the link is not working. Would need someone who understands server side of things so file the issue so that when the user click on the logo located on www.example.com/blog/ then it takes the use to www.example.com