The beginning sounds like "Why Raeliana Ended Up at the Duke's Mansion", but other than that I have no clue. I am still going to try and help though...
So basically: The male lead is blonde, and turned back time to save the female lead (who has brown hair, and is not the original character anymore) after the female lead (who has brown hair?) saves him from attackers in the forest or on a cliff. However in the original story the male lead (blonde man) fell in love with a red haired woman who is powerful and new to an academy?
Just trying to understand. Sorry for typing so much, please clarify if I have something wrong.
Actually is it "For Stella"?
https://www.mangago.me/read-manga/for_stella/

Hi! I remember reading about a girl who is reborn in another girl's (brown hair) body from a story where the girl now a secondary character who dies saving her childhood friend (blond guy) from the attackers somewhere in the forest or a cliff and he apparently also turns back in time and now understand how important that girl was and loves her now. But in the original story he fell in love with I believe red-haired girl who has big powers and is new in the academy. I remember a moment where red-haired even feels hurt when he is cold with her and says something along the lines "I feel like I lost something that was mine". There was secondary guy (black hair I think) who loves the red-haired girl. And the main girl also met another person who traveled into the story and teaches at the academy (white hair I think)
I have no idea how to find this manga and AI cannot help me.