Your cleans are fully flexible until 18:00 the day before the clean - you can reschedule, skip or cancel any clean in your Housekeep account or app before this time without incurring any charge.
Here's more info on how to edit cleans: How can I edit my cleans?
If you need to cancel or reschedule a clean after 18:00, or if your Housekeeper arrives and is unable to gain entry or start the clean, you will be charged the full price of the clean.