Need to clean the lower domain record

[ABC6]

I have a requirement where i need to update the sys id of top domain to lower domain in an override field , instead of updating record , it delete the sysid from override field, please help me to expedite .

var gr = new GlideRecord('sysevent_email_action');
gr.addEncodedQuery('active=true^sys_overrides=03973320c0a801020075d86be149dcbb^name=Email assigned to group');
gr.query();
if(gr.next()) {
gs.print(gr.sys_overrides);
gr.sys_overrides="b3dcb178db2bb348da52a2bc0b96198e";
gr.update();
}