Generally, How we could convert the closed form solution to an an iterative form?

Answer 1

Analyze the soln and see whether it admits of recursion. That is a sure sign that it can be broken down into an iterative form.

Answer 2

That is usually pretty easy. The trick is to go from iterative form to a closed form. All you do is just write down a first few terms. If you are talking about a specific series/sequence, put it up here and I'll see what I can do.