If your song has passed 1 million streams or is being released by a major label, the releasing artist or label must register the song with their PRO (ASCAP, BMI, SESAC, etc.).
When they register the song, they must include the WAVS sample creator and their publishing split as part of the registration.
If you’re only the producer (and not releasing the song), you do not register anything with a PRO — just pass the split information to the artist or label.