@1dusjhyahnt Use this and let me know if further assistance is required

var grInc= new GlideRecord('incident');

grInc.addQuery('sys_id',input.sysid); //considering you are fetching the number or sys_id from the HTML side

grInc.query();

if(gr.next()){

grInc.description = input.description; // fetching the input in the description field from HTML

grInc.update()

}