In openerp7, we used in many models, a button 'Assign to' to change assignment for message and notification, to another id model and even to another models.
Odoo 13 CE keep only the widget star 'TO DO' instead of the last three buttons 'TO DO', 'Move to Inbox', and 'Assign to'.
Where can I find again these functions ?
These functions have been remove from V13. To use them again, you must by a extra addon