Set form value in jQuery

I want to set the form value of a custom field in add-listing page.

Code is attached.

I have tried this, on wp_footer, not working,

<script>
jQuery("#reg_field_dis_am input").val('Value here');
</script>

and

<script>
jQuery("#reg_field_dis_am input[name=custom[dis_am]]").val('Value here');
</script>