Добавил модель User и прописал в MobileContext

Lesson49/Models/Data/MobileContext.cs

@@ -7,6 +7,7 @@ namespace Lesson49.Models.Data
         public DbSet<Phone> Phones { get; set; }
         public DbSet<Order> Orders { get; set; }
         public DbSet<Brand> Brands { get; set; }
+        public DbSet<User> Users { get; set; }
         
         public MobileContext(DbContextOptions<MobileContext> options) :base(options){}
     }

Lesson49/Models/User.cs

+namespace Lesson49.Models
+{
+    public class User
+    {
+        public string Name { get; set; }
+        public string Surname { get; set; }
+        public int Age { get; set; }
+
+        public override string ToString()
+        {
+            return $"Name - {Name}\nSurname - {Surname}\nAge - {Age}";
+        }
+    }
+}
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