Seacove shows you one Discover deck, not a menu of modes to pick between. It includes everyone within reach: crew on your own ship, crew on the ships tied up beside you, and crew ashore in the same port. There’s nothing to switch on or upgrade to see more of it.
The deck skips anyone you have already swiped on and anyone who has blocked you or that you have blocked.
You have a set number of swipes and likes over a rolling window, currently around 40 swipes and 10 likes every 12 hours. This resets on a rolling basis, not at midnight, and the exact number can change.