I have never been able to get Optimus Manager to work properly myself. I still use @dglt Optimus Switch program that he wrote for MJ on an Arch install. It can be completely set up using a TTY if you can’t log in.
For Gnome:
In order to use it with EnOS, you need to install the nVidia driver using their tools. You can do this by: sudo nvidia-installer-dkms
Once you have the driver installed, you can follow the rest of the instructions as written. If you want a GUI/ Indicator for Optimus-Switch, I have written a little program. Even though it still says Manjaro in the description, It still works on Arch and EnOS. Removing the MJ reference is still on my list of things to do. You can find it here:
WARNING Make sure you uninstall Optimus Manager completely before installing Optimus-Switch.