In some situations the Citrix Receiver will not delete saved credentials, resulting in the inability to logout and sign in with an alternate account.
This can happen with the Sierra MacOS and later versions of the Citrix Receiver, (12.7 or higher)
First, right-click the minimized Receiver icon, choose preferences, and Delete Passwords.
Clicking Log Off will not change the signed in username
Open Utilities and choose Keychain Access
Locate the entry for Citrix XenApp and delete any stored information
Go back to the Citrix Receiver, try clicking on any of the company icons. You will get a prompt to authenticate.
Keep in mind the domain\username in the following format:
Internal.skyboxonline.com\CompanyUser
The icons should now be active and will log you in as the user entered above. Click the + on the left side to add additional favorites, and then drag the DM icon to the desktop to further automate the login process.