You can replace I recently heard that ... with an expression such as John told me yesterday that ..., so this can be regarded as an instance of reported speech.
As to the tense, it is possible you have learned some rules about backshift which makes you uncertain which tense to use in the reported clause. Swan, in Practical English Usage, has some useful advice here:
Words that are spoken or thought in one place by one person may be
reported in another place at a different time ... . Because of this,
there are often grammatical differences between direct and indirect
speech. These changes are mostly natural and logical, and it is not
necessary to learn complicated rules about indirect speech in English.
So if Mary told you:
John went to Paris in 2000
you would naturally report this back to John as:
I recently heard that you went to Paris in 2000.
The past perfect is used to emphasise that something happened before another past event. So this is possible:
I recently heard that you had gone to Paris for a few months in 2000
before starting your new job.
But even here I suspect that most native speakers would use the simple went.
Under some circumstances, you can use "while I was there... " to describe what you did while you worked for an organization, but it depends on the organization and the context whether it sounds OK.
First, the context: while relates to a period of time. Of the following examples, the first two are OK, because the preceding sentence states or implies that a period of time is involved. The third is not so good because it only specifies a start, and the fourth is not good at all because it does not say anything at all about time.
I worked for worked for Monsanto about ten years ago. While I was there, I....
I worked for worked for Monsanto between 2005 and 2009. While I was there, I....
I joined Monsanto in 2005. While I was there, I...
I joined Monsanto. While I was there, I...
Concerning the organization: companies (even multinationals like Monsanto) seem to imply a place, so it sounds natural to use there. Organizations like UNICEF or the army do not imply a place, so there do not sound right. It would be better to say:
While I was with UNICEF...
While I was in the army...
Best Answer
Using "need" like that is a little old-fashioned, but still widely used. It comes off as very proper/fancy.
Since you say in the title that you want to tell the person that there was no need to (ever) worry, you need the past tense.
The most obvious and native-sounding way of saying this to me would be:
It is a bit idiomatic as "nothing to worry about" is a very common phrase. It sounds very natural.
If you want to use "need" specifically, I would say:
Saying "he need not worry" is perfectly grammatical and easy to understand. It just sounds very formal. Most people would just say "he doesn't need to worry." You can read more about that here.
There is maybe some syntactically valid way of phrasing it like "so you need not to have worried" but it sounds very awkward to me, and it takes some effort to understand someone saying that.