Hi
I am not sure if you mean that you cannot find the settings for call forwarding
or
that it does not work even when set up.
If you have made the settings, your phone is connected to your carriers network and the forwarding still does not work, it is a carrier issue and you should call them.
The exact location of the settings may differ on your S5 but they will be found by some thing like:
Open phone dialer
menu
settings
call
more settings (wait for the phone to read the network settings)
call forwarding