It is not possible to cancel an order from RusHour, so you will need to contact the delivery platforms directly:
For Uber: +44 (0)808 178 5518
You'll need to give them the telephone number associated with your account.
For Deliveroo: +44 (0)207 138 9037
You'll need to give them the Resto ID, which you'll also find on the tablet, by clicking on the Deliveroo order.
For Just Eat: +44 (0)208 736 2000