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.