See this article: Where is the Registrant List located?

1. Scroll down to the registrant data section
2. Select the registrants that you want to edit by clicking the checkboxes in the blue column - the checkbox at the top of the blue column, in the column label row, will Check All or Uncheck All checkboxes
3. Click the Bulk Edit button to choose the field that you want to edit

In this example, we are going to edit the Attended field.

Select the Attended field in the dropdown list. In this example, we are going to mark all checked registrants as Not Attended.

Note the names of fields that are automatically included in the menu. There are registrant settings, registrant details (About You fields) and further down, your survey questions.

The confirmation screen displays a list of all registrants that will receive this change.

• If the list is correct, click the Continue button
• If the list is not correct, click the Close button and revise your criteria

Since we moved the Attended column to the front of the list, it is easy to see that all 4 have been changed to Not Attended (No).

Have a look at this article: How Do I Bulk Delete Registrants?