Let’s say you have a repository structure like below (eg. because previously it was SVN repository where everything was on one place).
Now you would like to move example.com to separate git repository.
First of all, you need to install git-filter-repo.
# Clone old repository to new directory
git clone OLD_REPOSITORY example.com
# Remove everything else except example.com directory
git filter-repo --path example.com/
# Make example.com new root directory
git filter-repo --subdirectory-filter example.com
# Push to a new repository
git remote add origin NEW_REPOSITORY
git push -u origin master