Configure a bulk operation to apply a tag to your subscribers that have received a particular broadcast.
If you are unfamiliar with bulk operations, please check out this article!
Create a new bulk operation:
Select the Choose a segment of existing subscribers option:
Apply the filter that will return only the subscribers that have received a particular broadcast:
There are other options within the above filter besides the has received parameter:
Apply the tag:
Click the Next button to schedule when the bulk op should be performed.