think pocketmine has built in world changer /world worldname if not go to Plugin Tools click on phar to zip archive, extract the zip to folder, edit plugin.yml and change to new api, save and rezip. go back to Plugin Tools and do zip to phar, rename the phar file and you're done
i already changed the api and rename it to "manyworld.zip" and i got this error Error: Failed opening ZIP ER_NOZIP(): This is not a ZIP file
I have a plugin called WorldShift that can help you https://poggit.pmmp.io/ci/jasonwynn10/WorldShift/~