I would start by removing the battery pack from the scooter.
Next I would remove the speed controller and if it has an end on it held on with screws remove the end to allow the controller to dry out. Then shake any water out of the controller that you can and place the controller in a hot place or in the sun to allow it to completely dry out before reinstalling it. It is very important the there is no moisture at all in the controller before reinstalling it. I would also remove the throttle and shake any water out of it and allow it to dry out in a warm place also.
On most electric scooters the controller and throttle are the only parts that have sensitive electronics inside of them that need to be dry. If the scooter has a speedometer or battery meter on the handlebars then they should also be allowed to dry out before running the scooter again.
Please let us know how it goes.
I have a similar problem but it wasn't caused by riding the scooter into a swimming pool, just a rainstorm was enough to wet the electronics. The only symptom is I cannot turn my headlight off. It occurred once before and I disassembled the control panel and dried it out.
Just an afterthought. Don't try to speed up the drying out process with a hair dryer, they run very very hot and can melt plastic.
Gee it must have been some party, who drove the scooter into the pool ?