https://unix.stackexchange.com/questions/53784/how-can-i-reinstall-network-manager-after-uninstalling-it

systemctl restart NetworkManager

yum install NetworkManager

Check if running or Start if not:

service NetworkManager status

Start if it's not running:

service NetworkManager start
chkconfig NetworkManager on

Disable network and wpa_supp services as stated in Wiki:

chkconfig network off
chkconfig wpa_supplicant off

And Reboot. To open it's GUI:

nm-applet
nm-connection-editor