From Signitic, you can make actions on all your users in the same time thanks to the grouped actions bar.
From the menu "Users" accessible from the left sidebar, select your users with the checkbox on the left of each row or filter your users with the list buttons on the top.
Then click on "Mass edit" from the grouped action bar:
You will now be able to choose one value for a field for all the users you selected.
Hit the confirm button and it should do the trick!