Hi! [Serial number for Cloud subscription]

Creative Cloud subscriptions/products do not have serial numbers.

Download/install the desktop application, sign in, install the subscription application(s).
https://helpx.adobe.com/creative-cloud/help/download-install-app.html

Creative Cloud for desktop
https://helpx.adobe.com/creative-cloud/help/creative-cloud-desktop.html

Sign out, Sign in | Creative Cloud desktop app

http://helpx.adobe.com/creative-cloud/kb/sign-in-out-creative-cloud-desktop-app.html