Fresh install of GitLab-CE, carry over old repositories and settings

I have a fresh install of Ubuntu 16.04 Server on which I’d like to install GitLab and would like to restore the repository I was working . I’d like to do the following:

  1. Move all the gitlab related data form the old hardrive to an external drive on /mnt
  2. The original repo used apache2, I’d like to use the bundled nginix instead.
  3. How do I simply transfer the repository data and the user/group data. I would not like to carry over web server information or runner informations.

Where do I start?

When I tried relocation the files, using this:

[execute] psql: could not connect to server: No such file or directory
              	Is the server running locally and accepting
              	connections on Unix domain socket "/var/opt/gitlab/postgresql/.s.PGSQL.5432"?