git clone --mirror <old-repo-url>
cd <repo-name>
git remote add new-origin <new-repo-url>
git push new-origin --mirror
git checkout your_branch_name
git filter-branch --prune-empty --subdirectory-filter relative/path/to/subdirectory your_current_branch_name
git remote set-url origin https://github.com/ao/your_new_sub_repo.git
git push -u origin your_current_branch_name