Hi Balram,
Two ways you can achieve it.
1) From Employee htmpl forms on detail_in.htmpl\detail_cr.htmp, comment the below lines.
// if (!bUseTransitionButtons) {
// ImgBtnCreate("btn003","Reopen_Incident", "reopen_incident()", "defer", 0);
//}
2) Employee Data partition on pre-update constraint type on call_req to have additional where class as status !='CL'.
Regards,
Mohtesham