@niveditakumari 

it worked see

Script Include:

var ValidationUtils = Class.create();
ValidationUtils.prototype = Object.extendsObject(AbstractAjaxProcessor, {
    validateDate: function() {

        var selected_date = new GlideDateTime(this.getParameter('sysparm_expectedDate'));
        var requiredDate = new GlideDateTime(); // Todays Date
        var businessDays = 7;
        var daysAdded = 0;
        while (daysAdded < businessDays) {
            requiredDate.addDays(1); // Move to the next day
            var dayOfWeek = requiredDate.getDayOfWeek(); // 1 = Sunday, 2 = Monday, ..., 7 = Saturday
            if (dayOfWeek != 6 && dayOfWeek != 7) { // Exclude Friday (6) and Saturday (7)
                daysAdded++;
            }
        }
        var output = {};
        if (selected_date.getDate() > requiredDate.getDate()) {
            output.correctDateSelected = 'Yes';

        } else {
            output.correctDateSelected = 'No';
            output.requiredDate = requiredDate.getDate().toString();
        }
        return JSON.stringify(output);
    },
    type: 'ValidationUtils'
}); 

Client Script:

function onChange(control, oldValue, newValue, isLoading) {
    if (isLoading || newValue == '') {
        return;
    }

    g_form.hideFieldMsg('my_datetime');

    var validateSelectedDate = new GlideAjax('global.ValidationUtils');
    validateSelectedDate.addParam('sysparm_name', 'validateDate');
    validateSelectedDate.addParam('sysparm_expectedDate', g_form.getValue('my_datetime')); //Replace your date time variable
    validateSelectedDate.getXMLAnswer(function getExpectedDate(answer) {
        var validatedOutput = JSON.parse(answer);
        if (validatedOutput.correctDateSelected == 'No') {
            g_form.showFieldMsg('my_datetime', 'kindly select date after ' + validatedOutput.requiredDate.toString(), 'error');
        }
    });

    //Type appropriate comment here, and begin script below

}

Output:

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