If players want to have K.K. Slider visit their city (thus enabling terraforming in Crossing the Animals: New Horizons in Change, they will need an island with 3 stars city rating or more.
You will be able to check your island rate when your Resident Services tent is upgraded to a building. To do this, just talk to Isabelle and make a choice "Let's talk island hopper." He'll give you a star rating, repeat some response from an unknown character, and then explain what you need to do to improve your island.
With an average of 1 star, he'll just tell you that your island needs more tourists staying there. You will need to talk to Tom Nook and book additional real estate if you do not already have a 10-acre site on your island.
Each building costs 10,000 Bells, but you'll get Nook Miles at the post every time a new person comes in. If you have found many people living on your island, you will get a 2 star rating. It doesn't require 10 full residents, so just check back with Isabelle whenever the new one comes in to see if you've made it 2 stars.
Once you have 2 stars, Isabelle will give you tips on how to increase your star rating. Possible objectives include:
- Plant more trees
- Plant more flowers and make them bloom
- Decorate your town with lots of furniture
- Build an extra wall in your city
- Build more tendencies and bridges
- Build more facilities (such as a museum or an attachment store)
You can go further than that. For example, if you have too many trees growing on your island, Isabelle will let you know that it's time to cut down some.
Keep a look back with Isabelle as you make the transition to the island. Her assessment may change on the same day, so if you see her stop suggesting a specific goal, then you have accomplished the requirements and can move on to another.
If you have 3 stars, Isabelle and Nook will let you know that K.K. Slider is on his way to the concert and will arrive the next day. After he makes and pays the bills, you will unlock the ability to use your island. Finally!