I assume you mean for how I pulled this off? well,
I made my nichelings completely prepared for the island. heat body, swimming genes, speed genes, and some cosmetics just for fun. I should have given them a normal tail instead of swimming for an extra heat resistance because the frost lands can get too cold, even for these fellas.
I then made a male and a female. I should have made multiple couples to start the island off right, but whatever. it works regardless.
I turned off all damage, removed all animals and (most) plants, turned down every age slider except for adulthood, which I extended, so we would have nichelings for as long as we could. so they can move around the island and not be harmed by anything.
once I opened the game, I used cheats to give us as much food as we could. going to high can cause the food to go in the negatives and can cause a lot of problems, so to be save I just input 'BerryCount 123456789'. although they cant starve to death, this prevents a lot of lag. the one thing I cant really prevent is illness, however.
next, to start breeding, I put a single male in a circle surrounded by other females, and have them breed every day. once the children are born they can immediately move out of the nest and I can breed again. once old enough, I can send them to fill up the ocean first. once the ocean is full, I can start filling the whole island. (what I'm doing right now)
I haven't finished, but its been working well so far, so I suppose this is the best strategy. once I'm done I'm going to attempt the archipelago, as I believe its bigger than the frost lands.
(The random genes you see everywhere are because my friend, during a call, suggested I give each area a different gene, like horns or fur color or snouts.)
(Also also, some times I changed the weather to get rid of snow. This caused a little glitch in the day counter that said we had more days on the island than we actually did, but it didn't effect the game so I ignored it.)