"is"

OD, I have now read this six times and I cannot understand what you are trying to say.

Where would this go?

I cannot find the verb that goes with "the content posted in EnglishForward.com site"? (I would rewrite that, but I don't yet understand what I'm rewriting.

Please note that ... okay
the content posted on the site www.EnglishForward.com -- okay

Then

My apologies. I posted some threads (related to the personal statement) in the forum. And I want to let the university know that those contents are mine.

So do you want to add this to the end of your personal statement sent to the university so they know that if they google it, they will find your posts? You don't want to be accused of plagiarism.

Maybe something like "Please note that you will find portions of this statement on the web site www.EnglishForward.com under my user name Odessa Dawn, as I sought input from native English speake

Yes to your question.

Please one thing:

under my user name Odessa Dawn

The applicant wrote the original content. And I, Odessa Dawn, posted it here for correction. Would you delete the word "my"? We helped each other using one user name. It was a huge task.

You are two different people?

Then yes, "the" user name.