Once the call has been accepted the page will be showing

Click on the Transfere button on the screen showing

Once the button is keyed in it will then show you the above page to decide how do you want the transfere to be done:
Transfere now - means blind transfere where you dont need to speak to the person you transfering to
Speak first - means you need to speak to the person first before you can send the call.

Once the transfere button is keyed it will pop out this page.
- either to add the number or to select the number from the list.