When using User/Device licensing in Citrix, licenses are occupied for up to 90 days, which is a long time if you have a limited amount of licenses. If you need to release them, here is how you can do it:

• Stop the service Citrix Licensing Service, Citrix License Config Service and Citrix Support Service
• Delete the following folder (or rename it, just to be sure): "C:\Program Files(x86)\Citrix\Licensing\LS\resource\cache"
• Start the service Citrix Licensing Service, Citrix License Config Service and Citrix Support Service
• Enjoy

References:

https://ulrikchristensen.com/how-to-release-unused-citrix-user-or-device-licenses/