Dial 072 on the telephone you wish to forward. You will be prompted by the follow message.

"Please enter the phone number to forward to and press pound # or press pound # to cancel forwarding"

Type in the number you wish to forward the phone to.  The number can be another extension number or a full telephone number.

The forwarding menu will respond "Call forwarding has be set to" and it will read back the number to you before hanging up the call.

Dial 073 to cancel Call Forwarding. 

The above procedure is for forwarding a single phone. If a phone is part of a ring group, it will not forward calls that come in to the ring group.

See article How to program a forward extension for a ring group.