Change Master Branch To Directory Of Imported Repo

I am having an issue that I can’t seem to find an explicit answer to. First, a little background. I have received a GIT bundle which was created from an SVN repository. I was able to import it fine and have 181 commits with only one branch pointing to the top of the directory structure. This is named the master branch, co there are no real structural or import issues that I know of.
What I am trying to do is set the master branch to a directory four levels deep. I had found instructions on creating a new branch, but it still points to the upper level directory instead of the desired location. I had also found instructions for setting the HEAD using GIT on the command line. I have a local Ubuntu server hosting our Gitlab CE instance and tried to CD into the directory where the desired repo is stored, but can’t get into that directory.
It seems like this should be a simple process, and I am probably just missing an obvious step. Can someone help in resetting the master branch to a directory in the repo?