Download CustomSounds.rar from Google Drive.
Extract it into your World of Warcraft\_retail_\Interface\AddOns file.
https://drive.google.com/file/d/14Nfrj1p9MlsT4ml7h4EhJBhpxzGkMuU1/view?usp=sharing
If you want to use it on other immunity abilities, pls change the spell ID in the WeakAura>Trigger 1>Exact Spell ID(s).