From Signitic, you can make actions on all your users in the same time thanks to the Grouped Action button.
From the menu "Users" accessible from the left sidebar, select the checkbox at the top left of the user table.
Then click on the "Grouped action" button and select "Mass edit".
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!