I got the result by below script.

//Client callable script include

var BusinessDays = Class.create();
BusinessDays.prototype = Object.extendsObject(AbstractAjaxProcessor, {

    Bdays: function() {
       
        var temp = new ExcludeHolidays().holidays();  // getting last business day (considering 30 business  days) refer script below.
        var array = [];
        var c = 0;
        var gr = new GlideRecord('incident');
        gr.addEncodedQuery('sys_created_on<' + temp);//assignment group Parent is AAFR_XX_CG_ComputaCenter
        gr.query();
        while (gr.next()) {
            array.push(gr.number.toString());
        }

        return array;

    },
type: 'BusinessDays'
});
 
 ============//getting last business day from today(30 days ago)
var ExcludeHolidays = Class.create();
ExcludeHolidays.prototype = Object.extendsObject(AbstractAjaxProcessor, {

    holidays: function() {
        var count = 0;
        var tday = new GlideDateTime();
        var temp = tday;  //temporary variable

        while (count < 30) {

            if (temp.getDayOfWeekUTC() != 6 && temp.getDayOfWeekUTC() != 7) {
                count = count + 1;
            } //excluding weekends

            var schedule = "US Holidays";
            var sch = new GlideRecord("cmn_schedule");
            sch.addQuery("name", schedule);
            sch.query();
            if (sch.isInSchedule(temp)) {

                count = count - 1;  //reducing count since last count was including holidays
            }

            temp.addDaysUTC(-1);  // reducing day by 1

        }
        return temp; // returning business day 30 days ago 
    },
 
 
//in the filter you need to add
Number is one of javascript&colon; new BusinessDays().Bdays();
 
 

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