How to call SeedRoles method in Program.cs

The SeedRoles class should be a static class, you can modify it as below:

//required
//using Microsoft.AspNetCore.Identity;
//using Microsoft.EntityFrameworkCore;
public static class SeedRoles
{
    public static void Initialize(IServiceProvider serviceProvider)
    {
        using (var context = new ApplicationDbContext(serviceProvider.GetRequiredService<DbContextOptions<ApplicationDbContext>>()))
        {
            string[] roles = new string[] { "Owner", "Administrator", "Tests2", "Editor", "Buyer", "Business", "Seller", "Subscriber" };

            var newrolelist = new List<IdentityRole>();
            foreach (string role in roles)
            {  
                if (!context.Roles.Any(r => r.Name == role))
                {
                    newrolelist.Add(new IdentityRole(role));
                }
            }
            context.Roles.AddRange(newrolelist);
            context.SaveChanges();
        }
    }
}

Note: In my application, the DB context is ApplicationDbContext, you can chnage it to yours.

Then, in the program.cs file, you can call the seed role method after the var app = builder.Build(); line, code like this:

// Add services to the container.
var connectionString = builder.Configuration.GetConnectionString("DefaultConnection");
builder.Services.AddDbContext<ApplicationDbContext>(options =>
    options.UseSqlServer(connectionString));
builder.Services.AddDatabaseDeveloperPageExceptionFilter();

builder.Services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = true)
    .AddRoles<IdentityRole>()    //enable Identity Role
    .AddEntityFrameworkStores<ApplicationDbContext>() ;
builder.Services.AddControllersWithViews();

var app = builder.Build();

using (var scope = app.Services.CreateScope())
{
    var services = scope.ServiceProvider;

    SeedRoles.Initialize(services);
}

The result as below:

More detail information, you can check the official document and sample.