Importing games back into steam [duplicate]

Solution 1:

According to this reddit thread, it should be possible to create a new steam library on the external drive, and then copy the games from the old install directory to the new library.

Yes. You have to make Steam create the directory first. Then copy the games into the directory afterward. It won't let you create the directory if it isn't empty. Then afterward just install games like normal and it will "detect already installed data" when it tries to install your game and jump to 99% and then complete.

Solution 2:

Go to Steam -> Settings, and find this button:

Click it, and you will see this:

Add the location of your old library found on your HDD there, and Steam will immediately recognize it.