On installing the Add-On in preferences in blender. Below message is showing ,
' upgrade to 2.8x '.
I dont understand which version is this.
Also, Chordata submenu not showing under windows drop down menu .
You are probably using a version of blender previous to 2.80. You can tell by looking at the version number on the splash screen.
There was a mayor update in blender at that version and many addons are not compatible with the previous ones.