Hi @nameisnani ,

Try below

Create Business rule :

Table - sc_task
When to Run - Before Update
Condition - item is Snow Support 
Scripts -

(function executeRule(current, previous /*null when async*/ ) {
    // Add your code here{
        GlideSysAttachment.copy('sc_task', current.getUniqueValue(), 'sc_req_item', current.request_item);
})(current, previous);

Thanks,

BK