If a restaurant hasn't accepted your order, you can cancel your order and place it again. Once restaurant accepts the order, you are not able to change items through the app.
In order to provide customer better experience, restaurants started preparing the food after accepting your order request. They would not be able to accept the changes in most of the cases. Please double confirm the items before you place the order.
Note that any accommodation of special instructions are at the discretion of the restaurant. There may be additional charges for adjusting your order.