Underwater Effect for Voice and Underwater Sound Effect
This might be common knowledge, but you can open your sound files in a program like audacity and add a low-pass filter and reverb effect to create a quick and cheap underwater
How to Create an Underwater Text Effect in Photoshop
MUFFLED/UNDERWATER AUDIO EFFECT - HitFilm Pro Tutorial - YouTube
Underwater sound effect - YouTube
What would be your most realistic effects chain to create an underwater effect? : r/ableton