The complete quote is:
Reality is created by the mind. We can change our reality by changing our mind.
Probably not. The first quotation as such for the sentence I found is in a 1990 book (Being Happy!) by Andrew Matthews. There is practically no Plato-context provided there; it a appears in a quick succession of quotes attributed to others (next one is supposedly from Marc Aurelius). According to Wikipedia that book sold 7 million copies in 42 languages though.
In my opinion, the quote is some kind of oversimplification (if not intentional distortion) of the allegory of the cave. But since no source that gives it appears to discuss the quote with more [Plato-]context, this is just my speculation. Actually, I may be too charitable in that regard. Matthews (p. 115--quote below) claims that Plato described thoughts as energy or vibrations, which as far I know, he didn't.
So for every time you produce a thought, with its own unique vibration, you must be producing a reaction or consequence. As you may have around fifty thousand thoughts a day, you're sending out a a lot of vibrations and producing a lot of consequences. What I wish to establish here is that thoughts are real forces. We're dealing with energy.
Plato spoke of these forces when he said : "Reality is created by the mind. We can change our reality by changing our mind." The Roman, Marcus Aurelius, wrote "A man's life is what his thoughts make of it." The Bible said, "Man is what he thinks about all day long ...
Just a quick search on the last quote there suggests that's also being misattributed by Matthews.