So you have to get 3 pieces of wood - 2 blanks beside the flower to be pollinated and beside the crafting hut, and 1 mini log above the farm.

Drag three adult villagers to each wood piece and they will put it beside the pier. Drag any three adult villagers to the pieces for them to fix it.

Once done, the trading boat will come to the raft. Collect your three lavastones!

There's also a dragon beacon which can be used to recall the trading boat.