You can't, unless you do it at filesystem level, eg. make a junction between the S2 install root within Steam's default/current game dir and wherever you moved the actual files to. Steam only supports one location per drive to be set as game storage.

If the issue is that Steam itself is installed in an unsuitable location (eg. Program Files) and the games are installed under it (which is the default), you can have the entire games folder moved to somewhere else by Steam itself and then everything will be updated accordingly, but you have to move S2 back to where it should be first.

Actually, moving the games folder is also only possible to another drive, unless you work around it manually. It's probably best to move Steam as a whole.

Here's how: https://steamhost.cn/help_steampowered_com/faqs/view/4BD4-4528-6B2E-8327

Theoretically it should also be possible to make a new dir and only move the steamapps (and userdata?) folders there, then start Steam, which will then behave as if no games were installed, then select that new dir as the install folder in Settings > Storage, then the client should realize there are games installed in it and update itself to use that dir as the install location from then on.