Go into the Phone settings, which can either be found by clicking the icon to the top-right of your contact list or through the pink coloured Settings icon on the homescreen.
Under Call Options, there should be a setting called “Configure call forwarding”. Press this and a pop-up will appear.
You can now amend your call forwarding based on your requirements, by moving the toggle to the right of each option on and off.
Each selection gives you the choice to enter in a number (e.g. mobile number) or select a contact from your contact list. If you select this option, it will take you to an alphabetical list of your contacts so you can select the person/group you wish to forward calls on to.
These settings give you the options to ‘always forward’ ‘forward when busy’ and ‘no answer forward’, giving you a range of choices for your requirements.