If you haven't heard already Wunderlist is going away on May 6, 2020. However you can save all your lists and tasks by importing them to Microsoft To Do.

Microsoft has made it pretty easy to import your stuff into Microsoft To Do. Just install it, login with the account you want to import to and go to the settings to select the Wunderlist account you want to import from. After that, it's pretty much sitting back and watching your lists and tasks import seamlessly into Microsoft To Do.