Hi all

So I saw an article / post on the website and now I cant find it. But went something along the lines of:
How to ask/what to say in a rehire letter

I've emailed this one agency, asked for a rehire forum but they havent replied yet.
So now I am wondering if there is a specific way one should go about to ask for this forum/letter and if any of you can assist on this matter?

Thanks in advance