If you've chosen Kanban, then the defaults will be not to put an estimate on screen for you - Kanban doesn't do estimates. (Well, actually, it does, but it's calculated - one card = one unit of work. Each card is an estimate unit and they're all the same "size")
I suspect that you've accepted the default settings and simply not added the estimate field you want to use to the screens and card displays. Your admins can do that for you.