Multiple Height maps in a Single level

I am currently making a little survival game and i have 1 main island, but im wanting to add more heightmaps for little island’s around this big one. Is there a way how i can add different heightmaps in a single level?
I have looked in the tab where i added my main island (In the landscape tab) But i only see the 1 Heightmap i imported.
If you cant have multiple heightmaps, is there a way how i can add these islands?