Once releases and lists are selected, the next screen will summarize both choices. If the lists are very long, click the Hide button to collapse a list and Display to reveal them again. 

Publish the assignment

Clicking Publish will make the releases available to the selected list. This process may take a few moments depending on the number of lists. 

Upon success, an email will be sent to your account summarizing the assignment and any errors.

Your successful bulk assignments will also show in the Assignments for those releases.