Existing Customized COPA characteristic to add check table

Hi,

I already have this customized COPA characteristic- tied to an operating concern. This COPA characteristic uses a customized data element.

Now I want to add a check table to it. I have already added a Value Table to the domain of the characteristic's data element. But in t-code: KEA5, the characteristic still does not show the check table under the 'Validation' section. Also in KEA5, it does not allow me to edit the characteristic.

Does anyone know how I can add the check table under the 'Validation' section in KEA5? Your help is very much appreciated!

Thank you.