A: 1) Turn it off
2) Remove the battery
3) Dry off everything as well as possible. Use some "dust-off" or other similar canned air products to blow moisture out of any place you can get to. Leave to dry at least 24 hours.
4) Re-install battery, cross your fingers, and turn it on. If you got to it before water got to the "brain" inside, all should be fine.
Most drones survive a bit of rain or an accidental dousing fairly well, but if they fall into a pool, lake, pond, river, etc. it depends how quickly you retrieve them. I have had several that actually were so light that they floated...
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