You will need to reach out to support to register your institution’s email domain. You’ll need to provide proof that your institution is legitimate, such as a letter from the administration or a link to the institution’s official website. Open a support request here:
https://azure.microsoft.com/en-us/support/create-ticket/
You can mark it 'Accept Answer' and 'Upvote' if this helped you
Regards,
Abiola