To fix on the website

the site has a banner that is duplicated on every page of the site. The attached link is misspelled and leads nowhere. In the admin panel is not possible to find this banner and fix the link (the admin webasyst). Because of this, every day multiply page with error 404 (at the moment they have about 5 789.

Should:
Find and delete the incorrect link. Post there a link in the required section.

Please let me know:
1.Cost;
2. Deadlines for eliminating problem.