Just let the baby latch on, might not get much the first few mins but it will cause another let down soon enough!

For me, if I let my baby latch on even if I feel like my boobs are pretty empty, within a minute or two of her sucking I feel another let down of milk. But I will also say that I produce a lot of milk normally, so I tend to "refill" within 15-20 mins after every feeding