ERROR: relation "decidim_system_admins" does not exist

Hi to everybody, this is the first time decidim app installation. I need help to solve this issue. I'm using instructions on github to install on Ubuntu 20.04. In the rails console I try to add decidim super-admin user. When i press enter to "user.save!" command i receive the ERROR: relation "decidim_system_admins" does not exist. Have you experiences about this issue? Have you solutions? Thanks in advance.