How to set bool value to true in MVC entityframework linq to entities

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LINQ

MVC5

entity-framework

Briefly

i'm creating a social site in MVC5..... I've a model User where i have some of these properties fname,lname,username,email,isNew...etc

so i have set isNew to false and when i press Login Button i have an if condition:

if(isNew==true) than redirect...to Index(A.M) Home(C) ....

else redirect....to NewUser(A.M) Steps(C)...

Now when i clicked Login Button its works pretty good i mean it redirect me to Steps(Controller) NewUser(ActionMethod) now here i want to set isNew value to true but i've no idea how to do this

What I have tried:

i have tried this below code...i just want isNew value set to true in

database when NewUser() Method calls 

public ActionResult NewUser(User model)
    {
        using (DbAccess db=new DbAccess())
        {

            var original=db.users.Find(model.uid);
            original.isNew = true;
              //var entry = db.Entry(original);
              //entry.Property(e => e.isNew).IsModified = true;
            db.SaveChanges();
        }
        return Content("Welcome");
    }

and


public ActionResult NewUser(User model)
        {
            using (DbAccess db=new DbAccess())
            {

                var username = User.Identity.Name;
               db.users.Where(m => m.username == username).FirstOrDefault();
               
                //var user = HttpContext.User.Identity.Name;
                //db.users.Attach(model);
                //db.Entry(model).Property(x => x.isNew).IsModified = true;
                db.SaveChanges();
                
                //var original=db.users.Find(model.uid);
                //original.isNew = true;
                //var entry = db.Entry(original);
                //entry.Property(e => e.isNew).IsModified = true;
                //db.SaveChanges();
            }
            return Content("Welcome");
        }