Help setting up ASP.NET Core Identity and SQL Server

using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Mvc;
using SalonML_API.Data;
using SalonML_API.Data.Models;

namespace SalonML_API.Controllers
{
    [Route("api/[controller]/[action]")]
    [ApiController]
    public class SeedController : ControllerBase
    {
        private readonly ApplicationDbContext _context;
        private readonly RoleManager<IdentityRole> _roleManager;
        private readonly UserManager<ApplicationUser> _userManager;
        private readonly IConfiguration _configuration;

        public SeedController(
            ApplicationDbContext context,
            RoleManager<IdentityRole> roleManager,
            UserManager<ApplicationUser> userManager,
            IConfiguration configuration)
        {
            _context = context;
            _roleManager = roleManager;
            _userManager = userManager;
            _configuration = configuration;
        }

        [HttpGet]
        public async Task<IActionResult> ImportLoremIpsum()
        {
            throw new NotImplementedException();
        }

        [HttpGet]
        public async Task<IActionResult> CreateDefaultUsers()
        {
            // create the Administrator role
            string role_Administrator = "Administrator";

            if (await _roleManager.FindByNameAsync(role_Administrator) == null)
                await _roleManager.CreateAsync(new IdentityRole(role_Administrator));