Which is after God spoke to Moses in the burning bush...
Here is Exodus chapter 6 and this is when Moses and the Israelites learned His name.
Exodus 6 (KJV)
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¹ Then the LORD said unto Moses, Now shalt thou see what I will do to Pharaoh: for with a strong hand shall he let them go, and with a strong hand shall he drive them out of his land.
² And God spake unto Moses, and said unto him, I am the LORD:
³ And I appeared unto Abraham, unto Isaac, and unto Jacob, by the name of God Almighty, but by my name JEHOVAH was I not known to them.
⁴ And I have also established my covenant with them, to give them the land of Canaan, the land of their pilgrimage, wherein they were strangers.
⁵ And I have also heard the groaning of the children of Israel, whom the Egyptians keep in bondage; and I have remembered my covenant.
⁶ Wherefore say unto the children of Israel, I am the LORD, and I will bring you out from under the burdens of the Egyptians, and I will rid you out of their bondage, and I will redeem you with a stretched out arm, and with great judgments:
⁷ And I will take you to me for a people, and I will be to you a God: and ye shall know that I am the LORD your God, which bringeth you out from under the burdens of the Egyptians.
⁸ And I will bring you in unto the land, concerning the which I did swear to give it to Abraham, to Isaac, and to Jacob; and I will give it you for an heritage: I am the LORD.