Thanks to a fishing string hanging from a powerline, I crashed my DJI Mavic 3 Classic in to the river.
I am sorry to hear that; fishing line, whether hanging from a tree or streaming under water, with one end hooked on a log, is one of the nightmares of all swimmers…
As for your drone, I hope you lost it in Fresh Water, not Salt or Brackish Water (the Salt will Permanently destroy it…). If it was "salted", you might get it working, but it soon die from internal corrosion…
The two rivers near me, the James River and the York River, are both brackish from the Ocean tides flotation.
I also hope you removed the battery immediately and did not try to restart it until it was completely dry else the water might have created a short that could destroy internal components.
If it was mine, I would immediately have tried to blow out as much moisture as possible (vacuum cleaner set on blow, verses suction) then I would have dumped a big bag of rice all over it to absorb the rest of the moisture and that might take a week or more…
I do not profess to have any idea if your battery is any good any more, but I would have also put that under the rice also…
I am guessing that since you are asking this question, you did not buy the Care Refresh Insurance or it has expired… If it is still active, I would seriously consider using it if the drone is inoperable.
If the drone is inoperable and you do not have any insurance coverage, you should start Googling for Drone Repair Facilities, contact them and get cost estimates for the initial inspection, they are not Free, they take time to evaluate a dead drone… If you are lucky enough to have one that you can drive to and drop off the drone, you are lucky, but if you have to mail it in, do not get wrapped around the one closest to you. One further away may be so much better qualified to repair the drone.
Be sure to do your Due-Diligence and check for reviews on line to make sure, they actually have good results… Some of these places are great at repairing phones, computers, etc… but are just hoping that someone will send in a drone so they can learn how to repair them, they have no experience nor any spare parts…
If they deem it reparable, make sure the repair estimate is not extra to the repair and is now free since you are authorizing a repair.
Worse case, you sell it on eBay for spare parts…
Good Luck!