Authorization missing for connected plant &1 and company code &2

What causes this issue?

You cannot change the plant and company code of a user who doesn't have
authorization for the particular plant and company code.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Contact system administrator.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.