Correct these method and suggest how to use them

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C#

TPL

 public List<CustomerModel> GetAll()
        {
            List<CustomerModel> customers = new List<CustomerModel>();
            db.Customers.ToList().ForEach(customer =>
                {
                    customers.Add(new CustomerModel()
                    {
                        CustomerId = customer.CustomerId,
                        FirstName = customer.FirstName,
                        LastName = customer.LastName,
                        Address = customer.Address,
                        CreatedAt = customer.CreatedAt
                    });
                });

            return customers;
        }

public async Task<List<CustomerModel>> GetAllAsync()
        {
           
            return await Task.Run((Func<List<CustomerModel>>)GetAll);
        }

public Task<List<CustomerModel>> GetAllTask()
        {
            return new Task<List<CustomerModel>>(GetAll);
        }

I am unable to call "GetAllTask" method with await keyword. please help and also suggest how to use and make pure awaitable methods.