From the District screen, select Teacher Flags.
In parentheses next to each flag name, you can see the number of teachers assigned to that flag.
Select the ellipses, then Assign on the preexisting Flag which you’d like to assign to a Teacher. Select the Teacher's Site in the list. Use the dropdown menu to select the site.
Select the teacher(s) who will be Flagged. When you’re finished, select Done.