org-html-home/up-format

org-html-home/up-format is a variable defined in `ox-html.el'.
Its value is

"
\n  UP \n |\n  HOME \n
"

Documentation:
Snippet used to insert the HOME and UP links.
This is a format string, the first %s will receive the UP link,
the second the HOME link. If both `org-html-link-up' and
`org-html-link-home' are empty, the entire snippet will be
ignored.

You can customize this variable.