This is what worked for me, it’s NOT what the documentation says but hey!
Using the material theme as the default, this should replace the logo on the heading bar in Horizon.
No need to run
./manage.py collectstatic or anything, just run this and hit F5 in your browser
cp /home/myadmin/logo.svg /usr/share/openstack-dashboard/openstack_dashboard/themes/material/templates/material/openstack-one-color.svg
The logo on the login page is a little different
cp /home/myadmin/logo-splash.svg /usr/share/openstack-dashboard/openstack_dashboard/static/dashboard/img/ python /usr/share/openstack-dashboard/manage.py collectstatic