Slide your finger down the display starting from the top edge of your mobile phone.
Tap Settings.

Tap Call.

Tap Call forwarding.

After a moment the current settings are displayed.

Tap one of the following options:
Always forward

Forward when busy

Forward when unanswered

Forward when unreachable

Key in the required number.
If you selected Forward when unanswered in step 2, you need to select for how long you want your mobile phone to ring before the call is diverted:

Tap the field below "Delay".

Tap the required delay.

Tap Enable.

Tap the Home key to return to the home screen.