Normally you can install it with:
sudo mhwd -i pci video-nvidia-455xx
That should add the extra modules for nvidia. If it is installed, then remove it and reinstall it:
sudo mhwd -r pci video-nvidia-455xx
sudo mhwd -i pci video-nvidia-455xx
Do this by booting a manjaro live disk and manjaro-chroot -a in a terminal if no tty is available.