Cqrs Complex commands for master detail tables

I have a CreateUserCommand that responsible for creating accounts.

   public class UserCommandHandler : ICommandHandler<CreateUserCommand>
    {
        private readonly IUserRepository repository;

        public UserCommandHandler(IUserRepository repository)
        {
            this.repository = repository;
        }

        public void Handle(CreateUserCommand command)
        {
            User user = new User();
            user.Username = command.Username;
            user.Password = command.Password;
            user.Email = command.Email;

            repository.Add(user);
            repository.Save();
        }
    }

But I have UserInRoles Table including (UserId, RoleID) columns. So I have to add user in a role after creation.

How to do this nasted operations with CQRS?