Phrase used by jordan peterson about "revealing" In his book 12 Rules for Life: An Antidote to Chaos (Peterson, 2018) has following quote:

If you will not reveal yourself to others, you cannot reveal yourself
to yourself. That  does not only mean that you suppress who you are,
although it also means that. It means  that so much of what you could
be will never be forced by necessity to come forward. This  is a
biological truth, as well as a conceptual truth. When you explore
boldly, when you  voluntarily confront the unknown, you gather
information and build your renewed self  out of that information. That
is the conceptual element. However, researchers have  recently
discovered that new genes in the central nervous system turn
themselves on when an organism is placed (or places itself) in a new situation. These genes code for new
proteins. These proteins are the building blocks for new structures in the brain. This
means that a lot of you is still nascent, in the most physical of senses, and will not be
called forth by stasis. You have to say something, go somewhere and do things to get
turned on.

I am puzzled what he means by word reveal above?
why would you not want to reveal (whatever he means) yourself? Can you give some explanations what you think?
References
Peterson, J. (2018). 12 Rules for Life: An Antidote to Chaos. Toronto: Penguin Random House. ISBN: 0345816021
Re-reading the whole quote and not just the first 3 sentences there does seem to be some ramblings which need citations to back his claims.
The crux of your question:

I am puzzled [with] what he means by [the] word reveal above?

why would you not want to reveal (whatever he means) yourself?
The first 3 sentences loosely refer to the concept of the johari window which I spoke about in another answer.
The basic concept of the johari window is that in order to reveal yourself fully to yourself (who you are) you need to reveal yourself to others.  There can be abilities you have, and maybe aspects to your personality, which are unknown to you but others may see if you allow them to see them.
As for why you would not want to reveal yourself, there can be numerous reasons.  One example was used by Peterson in the same part of the book (Rule 8: Tell the truth — or, at least, don't lie)

Consider the person who insists that everything is right in her life. She avoids conflict, and smiles, and does what she is asked to do. She finds a niche and hides in it. She does not question authority or put her own ideas forward, and does not complain when mistreated. She strives for invisibility, like a fish in the centre of a swarming school.

This person is hiding herself.  She is not revealing her thoughts and ideas, so therefore she is not revealing herself.
If she revealed her thoughts and ideas she would be seen and heard, therefore putting the knowledge out there that she can think for herself.
On the other hand, she may not see that she can think for herself.  Maybe she thinks her ideas are not going to be correct or even be considered.
To find out more about the concept of the johari window, the links in the other answer (linked above) could help.
After those first 3 sentences, the quote gives so-called explanations referring to genes in the central nervous system (CNS) which I cannot vouch for and feel maybe a bit far fetched, although I must point out that I am not fully conversant with the neuroscience.  The problem with this part of the quote is that nothing mentioned is referenced, just like the first 3 sentences.
What I have found through basic internet searches is as follows:

Genetics of the nervous system refers to the study of genetics affecting the development, physiology and functions of the nervous system and diseases thereof(nature.com n.d.)

 

Several diseases that directly affect the nervous system have a genetic component: some are due to a mutation in a single gene, others are proving to have a more complex mode of inheritance. As our understanding of the pathogenesis of neurodegenerative disorders deepens, common themes begin to emerge...(National Center for Biotechnology Information 1998)

Whether this part of the quote can be relevant to the situation may be answered by others here, but seeing as you haven't asked about that directly I feel a separate question would be needed for that.
##References
National Center for Biotechnology Information (1998). The Nervous System. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK22197
nature.com (n.d.). Genetics of the nervous system. Retreived from https://www.nature.com/subjects/genetics-of-the-nervous-system