[Django]-Adding fields for User in admin page in django

What you should do is unregister default User and register the UserAdmin:

from app.models import UserInfo
from django.contrib import admin
from django.contrib.auth.models import User

class UserInfoInline(admin.TabularInline):
    model = UserInfo
class UserAdmin(admin.ModelAdmin):
    inlines = [UserInfoInline,]

# below lines should be added
admin.site.unregister(User)
admin.site.register(User, UserAdmin)

Try deleting registering part of UserInfo

EDIT:
Try following this example which is a working one:

models.py

from django.contrib.auth.models import User
from django.db import models
from django.db.models.signals import post_save
from django.dispatch import receiver

class Profile(models.Model):
    STUDENT = 1
    TEACHER = 2
    SUPERVISOR = 3
    ROLE_CHOICES = (
        (STUDENT, 'Student'),
        (TEACHER, 'Teacher'),
        (SUPERVISOR, 'Supervisor'),
    )
    user = models.OneToOneField(User, on_delete=models.CASCADE)
    location = models.CharField(max_length=30, blank=True)
    birthdate = models.DateField(null=True, blank=True)
    role = models.PositiveSmallIntegerField(choices=ROLE_CHOICES, null=True, blank=True)

    def __str__(self):  # __unicode__ for Python 2
        return self.user.username

@receiver(post_save, sender=User)
def create_or_update_user_profile(sender, instance, created, **kwargs):
    if created:
        Profile.objects.create(user=instance)
    instance.profile.save()

admin.py

from django.contrib import admin
from django.contrib.auth.admin import UserAdmin
from django.contrib.auth.models import User

from .models import Profile

class ProfileInline(admin.StackedInline):
    model = Profile
    can_delete = False
    verbose_name_plural = 'Profile'
    fk_name = 'user'

class CustomUserAdmin(UserAdmin):
    inlines = (ProfileInline, )

    def get_inline_instances(self, request, obj=None):
        if not obj:
            return list()
        return super(CustomUserAdmin, self).get_inline_instances(request, obj)


admin.site.unregister(User)
admin.site.register(User, CustomUserAdmin)

You can read more about it here.