To be able to make use of the Bits and Channel Points features provided by Twitch, you have to make sure you joined the Twitch Affiliate or Partner program.
If you are eligible and still can not set up Bits for your sounds, please do the following:
Please visit the Sound Alerts dashboard.
When logged in, please log out and re-login manually. This will ensure the system tracks your status as a Twitch affiliate/partner.
After logging in, you can set Bits for your sounds.