I assume that you're using Adobe Creative Cloud, and you're talking about Creative Cloud assets.
If you open the Creative Cloud desktop app, click on Assets, then click on Files. In that panel, if you click Open Folder, you'll see the files which are in your Creative Cloud assets (these are the copies on your local computer). You can drag other files into that folder, and they will be uploaded to the Creative Cloud.
You can also view the assets by clicking on View on Web. Your browser will open the Assets section of your Creative Cloud files. There you can use the Actions menu > Upload command to add files to the CC files.