You should just be able to copy the entire diablo 3 folder to the new location on your SSD.
Then, in the Battle net app, go to Options, then Game Settings:
https://i.imgur.com/Cv7t4Jb.jpg
Click on “Game Install/Update” and either choose the new folder by clicking “Use a Different Folder”
https://i.imgur.com/gh9QTdc.jpg
or click the “Scan for Games” button and click “Locate” if it doesn’t find it automatically.
https://i.imgur.com/vt3tP67.jpg