Hi, Gimnii
Good day!
Thank you for posting to Microsoft Community. We are glad to assist you!
According to your description, in a prepaid Microsoft 365 account, you can only remove licenses within seven days of purchasing or renewing your subscription -Kaufen oder Entfernen von Lizenzen für ein Microsoft Business-Abonnement | Microsoft Learn.
If you are outside this window, you won't see the option to remove licenses.
To reduce the number of licenses, you need to first unassign the licenses from users. Once unassigned, you should be able to remove the licenses from your subscription.
If you still can't find the option, it might be best to raise a ticket with the Microsoft Online Tech Support team directly - Support anfordern - Microsoft 365 admin | Microsoft Learn.
Note: Please be kindly to understand for our community team that we do not have the authority to access into the backend, thus, please refer the Microsoft Online Tech Support team for further assistance. Because they have the higher permission and able to assist you on the backend.
Thanks for your understanding in advance!
I hope this helps resolve the issue quickly! If you have any other questions or need further assistance, feel free to ask.
Thanks for your kindness and your understanding would be highly appreciated.
Wish you have a great day!
Sincerely,
Alex | Microsoft Community Moderator.