Try this:
1. For every file `/etc/*-release`, set the version value to 23.
2. Disable the fedora-rawhide repo (modify the `/etc/yum.repo.d/fedora-rawhide.repo` by setting `enable=0`)
3. In a terminal, do `dnf distro-sync`
4. If an error is thrown with package during this step and **only if** the package contains **f24** value on the name, do a `dnf remove
5. re-do `dnf distro-sync`
This solution should result in a valid Fedora 23 installation.