When you need to exchange the resources while participating in a Special Event, you can use the Converter.
To do that, find it on the Main Island of the Event.
Click on it, in the pop-up window in the upper part you'll see the number of resources that you will get after an exchange. Select an option that you want to receive.
Each chest requires a certain amount of resources for an exchange. For example, 1 bag requires 11 items. To add them into an exchanger click on the "add" button (green plus icon) in the upper corner of the item's icon.
Select the amount that you want to exchange and then click on the"OK" button.
You're almost there! When you add the required amount of the resources, click on the "Exchange" button.
The exchange itself takes mere seconds. After it's done, you'll see the corresponding chest near the Converter.