There have been many attempts to find the Trinity in the Old Testament. One of the most cited is the “Us” language used in Genesis. However, this was disproven hundreds of years ago by the rabbis.
The following is Rashi‘s commentary on Genesis 1:26:
“Let us make man: From here we learn the humility of the Holy One, blessed be He. Since man was created in the likeness of the angels, and they would envy him, He consulted them. And when He judges kings, He consults with His Heavenly household, for so we find regarding Ahab, that Micah said to him, (I Kings 22:19): “I saw the Lord seated on His throne, and all the host of heaven were standing by Him, on His right and on His left.” Now do “left” or “right” apply to Him?! But rather, [the passage means that] these [angels] were standing on the right to defend, and these [angels] were standing on the left to prosecute. Likewise, (Dan. 4:14): “By the decree of the destructive angels is the matter, and by the word of the holy ones is the edict.” Here too, He took counsel with His heavenly household. He said to them, “Among the heavenly beings, there are some in My likeness. If there are none in My likeness among the earthly beings, there will be envy among the creatures of the Creation. ” – [from Tanchuma, Shemoth 18; Gen. Rabbah 8:11, 14:13]. Let us make man: Even though they [the angels] did not assist Him in His creation, and there is an opportunity for the heretics to rebel (to misconstrue the plural as a basis for their heresies), Scripture did not hesitate to teach proper conduct and the trait of humility, that a great person should consult with and receive permission from a smaller one. Had it been written: “I shall make man,” we would not have learned that He was speaking with His tribunal, but to Himself. And the refutation to the heretics is written alongside it [i. e., in the following verse:]“And God created (וַיִּבְרָא) ,” and it does not say, “and they created וַיִּבְרְאוּ.” – [from Gen. Rabbah 8:9].”
These sources can be purchased here:
Sapirstein Edition Rashi: The Torah with Rashi’s Commentary Translated, Annotated and Elucidated, Vol. 1 [Student Size], Genesis [Bereishis]
Midrash Rabbah (10 Vol. Set)