How to add a value from one table to another table with django

The point is to make an accounting entry. I'm using the admin of django and when I create a seat I must use two accounts (which already exist in the table account) and those add or subtract the value that entered the seat (total), the thing is that I have been using python for 3 days and django and I do not know if this is possible or there is any way to do it.

This is the models.py

class Asiento(models.Model):
def __str__(self):
    return self.descripcion
id = models.IntegerField(db_column='ID', primary_key=True)  # Field name made lowercase.
fecha = models.CharField(db_column='FECHA', max_length=25, blank=True, null=True)  # Field name made lowercase.
descripcion = models.CharField(db_column='DESCRIPCION', max_length=25, blank=True, null=True)  # Field name made lowercase.
factura = models.CharField(db_column='FACTURA', max_length=25, blank=True, null=True)  # Field name made lowercase.
ctadebito = models.ForeignKey('Cuenta', models.DO_NOTHING, db_column='CTADEBITO', blank=True, null=True, related_name='debito')  # Field name made lowercase.
ctacredito = models.ForeignKey('Cuenta', models.DO_NOTHING, db_column='CTACREDITO', blank=True, null=True, related_name='credito')  # Field name made lowercase.
total = models.FloatField(db_column='TOTAL', blank=True, null=True)  # Field name made lowercase.

class Cuenta(models.Model):
def __str__(self):
    return self.descripcion
codigo = models.IntegerField(db_column='CODIGO', primary_key=True)  # Field name made lowercase.
descripcion = models.CharField(db_column='DESCRIPCION', max_length=25, blank=True, null=True)  # Field name made lowercase.
saldo = models.FloatField(db_column='SALDO', blank=True, null=True)  # Field name made lowercase.