Hello,

Please write an after update BR on sc_task with the below code:-

var count=0;
var tasks = new GlideRecord('sc_task');
tasks.addQuery('request_item',current.request_item);
tasks.query();
var taskcount = tasks.getRowCount();
while(tasks.next())
{
if(tasks.state == 3)
{
count++
}
}
if(count == taskcount)
{
var rq = new GlideRecord('sc_req_item');
rq.addQuery('sys_id',current.request_item);
rq.query();
if(rq.next())
{
rq.state = 3;
rq.update();
}
}

Please mark my answer as correct based on Impact.