Hi Bryan,

A big thanks for your support and your valuable time. It finally worked after making below changes,

Table - sysapproval_approver

Async BR

(function executeRule(current, previous /*null when async*/)
{
var gr = new GlideRecord('sc_req_item');
gr.addQuery('sys_id', current.sysapproval);
gr.query();
if(gr.next()) {
GlideSysAttachment.copy('sc_req_item', gr.sys_id, 'sysapproval_approver', current.sys_id);
}
})(current, previous);