Actually, you can't link that account.

Regular AWS Account won't be eligible for AWS Credits from AWS Educate as the email id should be issued from a School/College domain (i.e. SomeSchool.edu OR SomeCollege.edu)

If it's a regular AWS Student Account (enrolled prior to December 2019), then your friend would continue to receive the $100 AWS Credit as long as his academic year is valid, but again you can't transfer between 2 accounts, the Educate benefits are valid only for the original email id.
Earlier the case was different when the Credit Code was issued, you could use that code on any AWS Account, but with the new policy there is no alternate available other than the Student Starter Account.

At the most you can look for someone who has enrolled for AWS Educate in the recent past when the Credit Code was issued and if you managed to get hands on that Email Id when you would receive the code.