Hello,

Now a days getting migration certificate is a bit simple,  you can download it from the digilocker or if you don't find it there then contact to your respective school officials, they will able arrange it as soon as possible, or else,  contact to the CBSE officials by writing mail to them.

Hope you find this helpful.

P. S.  My suggestion is to contact with your school officials, it will be easier way to get the certificate.

Thank you!