Before proceeding, please be advised that this is not supported nor endorsed officially by CIP. Please refer to these official posts [1], [2], [3] and understand you will do this at your own risk.
All sound files are available in you Tibia folder, normally something like C:\Users\Name\AppData\Local\Tibia\packages\Tibia\sounds
Music files are easily replaceable as they have the distinct filenames ending in .ogg and they are not compressed. A simple drag and drop of a compatible file might do the trick.
Sound effects are slightly more complicated, as you will need to find the correct file, and replace the .wav in a way that the compression used by CIP doesn't become corrupted. Until the community comes up with tools to help with that - if ever - I would advise against touching them unless you have a clear reason to do that (such as a streamer might want to do that to entertain their audience).
Finally, keep in mind that all these modifications will likely be overwritten every time the client is updated.