If you've received an RX 6 Elements serial number from your Avid account page, below are some steps to get up and running:
1. If you haven't already, create an iZotope account:
https://www.izotope.com/en/create-account.html
2. On your iZotope account, click "Add by serial number" on the left-hand side of the Account Overview page:
https://www.izotope.com/en/account/serial-registration
3. Copy and Paste your serial number in here to register it to your account.
4. Then, you can download and install RX 6 Elements from the links below:
Mac Windows
5. After running the installer, open RX 6 Elements as a standalone application or within your host application/DAW.
6. To authorize, enter the serial number* from your account as well as the email address associated with your iZotope account. 
* Be sure there are no spaces at the beginning or end of the serial number or will be seen as invalid.