Dear sudharsan ps
Good day!
Thank you for posting to Microsoft Community. We are glad to assist!
Based on your description, I understand you concern with to set your existing Microsoft account as a student account.
It doesn't seem feasible to set your existing Microsoft account as a student account.
For student account, there is a school email address provided by your educational institution (e.g., ******@school.edu) who has Microsoft Education subscription.
School email address has their own domain which is set by educational institution or college.
On the other hand, to get student account, you can refer to Verify eligibility for Microsoft 365 Education subscriptions | Microsoft Learn.
If you have other questions, please feel free to let me know, I will continue to assist you.
Thanks for your precious time and your understanding would be highly appreciated. Have a nice day!
Best regards,
Allen | Community Moderator