Samsung Galaxy S6 edge

Find "Voice call"

Press Phone.

Find "Voice call"

Press MORE.

Find "Voice call"

Press Settings.

Find "Voice call"

Press More settings.
After a moment the current settings are displayed.

Find "Voice call"

Press Call forwarding.

Find "Voice call"

Press Voice call.

Select divert type

The current settings are displayed.

Select divert type

Press one of the following options:
Always forward

Select divert type

Forward when busy

Select divert type

Forward when unanswered

Select divert type

Forward when unreachable

Divert calls to voicemail

Key in (prefix) 5 (your phone number) and press ENABLE.

Return to the home screen

Press the Home key to return to the home screen.