It does sayAlone by Himself means the trinity is false. If God were a trinity it would say "Alone by themselves", at the minimum, but the Bible never says that; no, not once.
"26. And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.
27. So God created man in his own image, in the image of God created he him; male and female created he them."
Who was He talking to? look at vs.27. It went from our image (Three) back to one. Three in one, The trinity.
The we talking to each other only... alone. Only the Triune God could create man.