If you don’t control three or more creatures that share a creature type immediately after Littjara Kinseekers enters the battlefield, its ability doesn’t trigger. If you don’t control three or more as the ability resolves, you won’t put a +1/+1 counter on Littjara Kinseekers or scry 1. The three shared-type creatures you control when the ability resolves don’t have to be the same three you controlled when the ability triggered.