You can’t import specific assets currently but based on the latest features, that may be doable in the not too distant future. For now what you can do is either import the whole world or duplicate world. If you just want a small part of a bigger world, I’d recommend duplicating that bigger world. Then in the clone, delete all the stuff you don’t need. Once it’s ready, go to edit the target world. Once in target world, find the new semi empty duplicate in the my worlds menu and select import. Keep in mind that it’ll import it wherever it was on the map so you may need to hunt for it if both worlds aren’t in the same generic area.