Do not connect the power to the charge case. The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the case's operating design and could damage the components. The corrosion starts immediately and is ongoing until it is completely cleaned away.
You need to clean all the affected parts using Isopropyl Alcohol 99%+ (available at electronics parts stores) to remove all traces of corrosion and water. If possible do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain additives which may leave residues and is not as effective. If you do have to use it check the label to verify the amount of IPA. The higher the percentage of IPA the better.
Here is a link that describes the process. Electronics Water Damage
As always with electronics, especially surface mounted pcb be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board.
Here's a video that shows how to dis-assemble the buds and also the charge case, that will help. The charge case dis-assembly begins at approx. 8.00 minutes into the video.