These are the Libraries in the website.

If the library is not installed by Composer. then a manual install is performed.

In the folder /web/libraries create a fold of the library name ex: colorbox

Upload the downloaded zip file into the folder.

Expand the zip file. 

Open the folder created by the expand.

Select all the items in the expand folder and move them to the created folder .

Example move the contents of /libraries/colorbox/colorbox to /libraries colorbox