How do I edit an existing Validation?

Hi,

I need to edit a existing validation in place. There several steps to that validation.

The current validations reads as ( BKPF-BLART = 'SA' AND BSEG-HKONT IN ZSPL_VALID_TP I need to add another document type in addition to SA. Can someone tell me how do i go about doing this?

I tried going to insert & edit but it seems to add. Please can someone help me.

Thanks

Noopers