The possuk states Hashem said to Moses: “Come to Pharaoh, for I have hardened his heart and the heart of his servants…”
There is a question often asked. If Hashem hardened Pharoah’s heart then where was his free will?? Surely it meant that pharoah was not thinking for himself??
Actually the answer is quite the opposite. Hashem did harden Pharoah’s heart and his servants aswell, however the purpose of it was so that he had free will!!
I’ll explain, Imagine a manholding a gun to someone’s head saying “let the dog go or i’ll kill you”… Does the second man have free will?? you can argue yes he has free will but you are 99% certain he is going to let the dog go! therefore even though he has free will in reality the choice is only really to let the dog go!!
Here Hashem with Moshe and Aharon has a gun to Pharoah’s head saying “Let the Jews go”. He has crippled the country with 7 plagues so far. The country has never been anywhere near as powerful since before the plagues.
However because Hashem hardened Pharoah’s heart it gave Pharoah a choice to make, it was an equal 50% chance, shall he let them go or not.
That is why the Jews needed another 3 plagues before they were allowed to go!!