Configured objects: the assignment cannot be deleted

What causes this issue?

The class is used in <DS:GLOS.3526BF32AFAB52B9E10000009B38F974>Variant
Configuration</>.
The class is assigned to a configurable object (for example, material)
and the system has found that configured objects already exist for the
configurable object, such as sales orders or
<DS:GLOS.3526BF08AFAB52B9E10000009B38F974>material variants</>.

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

System Response

The assignment cannot be deleted.

How to fix this error?

To display a where-used list, choose <ZH>Display class -> Environment
-> Where-used list -> In configurations</>.
However, you can only delete the assignment with Engineering Change
Management.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.