Query ASP.NET identity (aspnetusers) table for the value in a custom field

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ASP.NET-Core

I've added to fields to the AspNetUsers table, the two fields (LastName and FirstName) appear in the database as expected. When I try to get the values in these two fields I receive red lines under the field names and error message indicating the fields cannot be found. What query will return the values. I can get the logged-in UserName, and I filter the query with it.

What I have tried:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
using Microsoft.EntityFrameworkCore;
using FSA.Data;
using FSA.Models;
using Microsoft.AspNetCore.Identity;

namespace FSA.Pages.Activities
{
    public class IndexModel : PageModel
    {
        private readonly FSA.Data.ApplicationDbContext _context;

        public IndexModel(FSA.Data.ApplicationDbContext context)
        {
            _context = context;
        }

        public IList<activity> Activity { get; set; }

        public async Task OnGetAsync()
        {

            // get user's Name (email address) from Identity (dbo.AspNetUsers)
            string userName = User.Identity.Name;

            // get users last and first name (fname) from Identity with userName as a filter
            var pubNameQuery = from n in _context.Users.AsNoTracking()
                               where n.UserName == userName
                               select n.LastName + ", " + n.FirstName;

            string fname = await pubNameQuery.SingleAsync();

        }
    }
}