I’m not sure I follow your line of thinking. Looking at Genesis 1:26,
‘Then God said: Let us make human beings in our image, after our likeness. Let them have dominion over the fish of the sea, the birds of the air, the tame animals, all the wild animals, and all the creatures that crawl on the earth.’
Here God refers to Himself in the plural form. While this doesn’t explicitly mean three, it does imply more than one.
We see this again in Genesis 3:22,
Then the LORD God said: See! The man has become like one of us, knowing good and evil!
The bible is replete signs of the Trinity and it has been an idea held from the very beginning of the Christian faith.