If you don't say whom you told, just use "say": "I said this when I was presenting something." A more specific verb may work, but you'd have to provide the context / desired meaning. (Note that the sentence, while correct doesn't actually convey any information. What is "this"? What is something?)

It’s not wrong but there is a verb which is unnecessarily in passive voice... better to say “is there anything else to add?”

The sentence is correct but not much information can be taken from it. What is "this" that you said "told"? Try to construct your sentences in a way that they speak to the other person. To me, this can not be a stand alone sentence. You must have said something (which in your sentence is "this") before saying that sentence. The use of "told" would be more fitting if you include a person's name. For example, I told Sam this when I was presenting the topic. But again, this can not be a stand alone sentence. I hope I am making sense.

It's good. You could also write "Is there anything else to add?" which means the same.

Does any thing else need to be added? I said this when presenting a topic.