Hi @Priya75 ,

You can refer below code 

var gr = new GlideRecord('u_test'); // your table name
gr.addQuery('patching', 'Sat 01:00 -4:00');
gr.query();
if(gr.next()){
	gr.week = <sys_id>; // sys_id of 3rd week record if this is reference field
	gr.update();
}

Please reach me out if you need anything. 

Please mark my answer correct and helpful if this works for you

Thanks and Regards 

Sarthak