Please see the video below (please note that the video is on a loop).
Please navigate to Settings->Yield Optimiser.
From the drop-down menu please choose the corresponding property.
Then press the Create New Rule.
Give your rule a name, for example "discount".
Choose the start and end date and then choose the price multiplier (hint: 90% means 10% discount, and 110% means 10% increase, etc.).
Please click Trigger and choose the corresponding rooms within a property and then choose Apply too and choose the corresponding property and rooms.