Incorrect EIN on investor K-1

What must be done if an investor, which is an LLC, transferred its interests to a different LLC and the EIN was not updated on the K-1 for tax purposes? The old EIN from the original LLC was used with the new correct transferee LLC name.

Does the whole tax return need to be amended or can you just amend the K-1 and reissue to the investor?

 

I am assuming the investor then needs to also do an amended return with the corrected K-1?

 

Thank you