I have a "Choice" column that uses a checkbox to add multiple items to a field in a list.  For instance, if an item needs attention by Joe and the Billing department, but not Mary, my workflow will send Joe and Billing a task, and check those boxes using a Build string that will concatenate all the items who need checked into a variable, and then update item with that variable into that field.

I'd like another step that will UNcheck these names once their task has been responded to, but I'm not sure how to go about it.  

Can someone point me in the right direction?