A Quick Tip:
How to rename your starred places on Google maps
Previously it could be done it normally, but now you that option is not there anymore. What you have to do is to go to Google Bookmarks (https://www.google.com/bookmarks/) and edit it from there.
This feature comes handy when you try to save an unnamed place or try to save an address/coordinate as something like the “Batcave”.
It will show immediately on your Android devices after saving on desktop or laptop editing. From Source.