Downgrade rights are typically limited to volume licensing, software assurance, and OEM partners. For OEM the downgrade is handled through the OEM (sometimes for a fee)
For volume center submit here.
https://support.microsoft.com/en-us/supportrequestform/2afa6f15-b710-db46-909a-8346017c802f?sl=en&sc=US
For SA you can submit here
https://support.microsoft.com/en-us/topic/microsoft-software-assurance-support-incident-submission-74a9a148-9a75-ecc8-4420-14191e634d65
--please don't forget to upvote and Accept as answer if the reply is helpful--