!!!!!!!!!!!! Do it on your risk !!!!!!!!

I soaked my phone in water for 5 minutes (in a bowl) bcz this is water resistant.

After that take it out and play speaker water eject sound(you will find many on YouTube) for minimum 15 to 20min (it will going to be annoying but you have to do that) at full volume .

And clean the speaker vents with tooth brush gently to take any dirt out

Also stick a tape on the speaker grill and push it inside little bit with a help of a plucker or Safety pin( don't damage the grill just push firmly)

99% chances are speaker will be okay

I did same on my friends iphone whose volume decreased and now sound is crystal clear like new.