Resolved: Combining two models into one in django

class User(AbstractUser):
    first_name = models.CharField(max_length=255)
    last_name = models.CharField(max_length=255)
    email = models.EmailField(unique=True)
    phone = models.CharField(max_length=12)
    username = models.CharField(max_length=150, null=True)
    company_name = models.CharField(max_length=255, null=True, blank=True)
    gst_no = models.CharField(max_length=150, blank=True, null=True)

class Address(models.Model):
    user = models.ForeignKey(settings.AUTH_USER_MODEL,
                             on_delete=models.CASCADE, related_name='address')
    street_address = models.CharField(max_length=100)
    apartment_address = models.CharField(max_length=100)
    country = CountryField(multiple=False)
    state = models.CharField(max_length=100,)
    city = models.CharField(max_length=100)
    zip = models.CharField(max_length=100)
    address_type = models.CharField(max_length=1, choices=ADDRESS_CHOICES)
    default = models.BooleanField(default=False)
    used_in_orders = models.BooleanField(default=False)
    display = models.BooleanField(default=True)

    def gst_no(self):
        return self.user.gst_no if self.user.gst_no else None

@admin.register(Address)
class AddressAdmin(admin.ModelAdmin):
    list_display = [
        'first_name', 'last_name', 'email', 'phone', 'username', 'company_name',
        'street_address', 'apartment_address', 'country', 'state', 'city', 'zip', 'address_type', 'default', 'used_in_orders', 'display'
    ]

    def get_queryset(self, request):
        queryset = super().get_queryset(request)
        queryset = queryset.select_related("user").all()
        return queryset

    def first_name(self, obj):
        return obj.user.first_name

    def last_name(self, obj):
        return obj.user.last_name

    def email(self, obj):
        return obj.user.email

    def phone(self, obj):
        return obj.user.phone

    def username(self, obj):
        return obj.user.username

    def company_name(self, obj):
        return obj.user.company_name

class Address(models.Model):
    ...

    class Meta:
        verbose_name = 'User Detail'
        verbose_name_plural = 'User Details'