I’ve seen your post and this is the tutorial on what to do just have a look at the picture below it shows which steps you have to take in order to migrate this pack into an existing project.
1 put the project into a convenient location
2 wait for the download to finish
3 open your project from the launcher
4 once your project is open right click on the landscape set in the directory and select migrate
5 in this window press okay
6 locate the content folder of your target project and select folder
7 now the content folder directory from the island pack has been moved after some time into your target project.
8 This however only moves the unreal content if you would like to transfer the height maps for later import locate them make the right click and go to show an explorer now you can essentially copy them to any location where you want to import them from in your future project.
9 You should now be good to go to put this package into any game that your desire.