Add virtual field in the sublist

 // Access the existing sublist,

                let sublist = form.getSublist({

                    id: ‘timeitem’ // This is the sublist ID for Weekly Timesheet

                });

                log.debug(“sublist”, sublist);

                // Add a new dropdown (select) field to the sublist

                let customSelectField = sublist.addField({

                    id: ‘custpage_custom_dropdown’,

                    type: serverWidget.FieldType.SELECT,

                    label: ‘Type Of Time’

                });

                customSelectField.isMandatory = true;