models.py

class User (models.Model):
  
  name = models.CharField(max_length=255)

class Manager (models.Model):
  
  registration = models.PositiveInteger()
  name = models.CharField(max_length=255)

class ClientHistory (models.Model):
  
  user = models.ForeignKey(User)
  
  # (...) other specific fields
  
  date_open = models.DateField()
  manager_open = models.ForeignKey(Manager, related_name="manager_open")
  
  date_close = models.DateField()
  manager_close = models.ForeignKey(Manager, related_name="manager_closed")