I gather that the form isn't meant to be a user interface at all, other than displaying the field agent and list of clients currently being faxed. That's a departure from the normal way a form is used. You might have said so.
Somehow the query is joining field agents with their clients. I'll assume this is a one-to-many relationship, though that's far from clear. And I'll assume that the tables are called FieldAgents and Clients, and the query join field in the Clients table is called FieldAgentID.
The list box holds data about clients, so I'll assume that you want to update a Yes/No field in the Clients table, which field I'll assume is called Sent. You originally seemed to be saying you wanted to update the data in the list box, but that makes no sense, because the data wouldn't be saved anywhere.
You can update all the Sent fields to Yes with a single SQL statement:
UPDATE Clients SET Sent = True WHERE FieldAgentID = (the ID of the field agent shown in the form)
You would execute this SQL statement after you finish faxing to one field agent. It would update all the clients at once.
There, now that wasn't so hard, was it? All I had to do was guess at the existence of a Clients table, guess at the existence of a Sent field in it, guess that the Sent field was what you wanted to update, and guess that the Clients table was related to a FieldAgents table via a FieldAgentID field. Of course, if you had told me this in the first place, I wouldn't have had to guess at all. Why did you think that concealing the relevant details made things simpler??? Rick Sprague