Start by mousing over the right hand end of the booking strip until the arrow changes to vertical parallel lines, now left-click and hold down to peel the booking back the required number of refund days. Let the click go to reveal the 'Refund Dialog'

Choose what rate you wish to use - Daily or weekly as per the rate editor or if you are using a different amount then choose 'Other'. If you choose 'Other' than enter the amount of the refund into the 'Total Amount' field. Click OK and proceed to the Tender Dialog.

NOTE:
If you wish to make the credited days (yellow bit of the booking strip) available for another booking, then simply peel back the yellow portion to the green.