Make new steam folder in storage drive, call it something you recognise like: Steam Games Folder.
open steam
settings
downloads
steam library folders top button
select/find/navigate to new folder (Steam Games or whatever you called yours) in storage drive.
remove other/old folder to ensure it only writes games to new folder (note you might need to re-install previous games that are already in the old location 'or possibly move them to new location and hope you can trick steam').