Before you can use Product Bundles editor you need to connect with the Content Glass account that was assigned to your store when you installed Content Glass app. This account has the user name match to your store domain, and a password that was presented to you when app was installed. You can always reset this password by going to https://www.contentglass.com/user/password and request new password.
The user that was created for you on the first time you installed Content Glass app is named: "managed-app admin". The managed-app admin has special permissions to access Contentn Glass services, including Product Bundles.
Note: Altough you can create new user from the login view, this user will not have the same credentials as your managed-app user.
To connect with CG account click the settings button and select "Social Accounts" from the main menu, or click the shortcut icon in case CG-Button is presented on your store. Click the "Connect" button nearby "CG" icon. The login dialog will open. Set the user/password you received upon installing the app.