Build a combo box for the sharepoint people/group field

I have a SharePoint list named Technicians which contain a field name "Technician Name" of type people/group, as follow:-

now i want to build a combo box field which shows the Technicians' display names to be able to search/filter the Technicians lists. but when i added a combox box field and i defined the Technicians inside the Items property i can not find the TechnicnainName field, as follow:-

Second question, Also i have a form for adding new Tasks >> and inside the form i want to show the list of Technician and pass the value of the selected Technician  to a field named AssignedTechnician field which is of type people/group also,, any advice?