Path of the file where searching email is Illuminate\Foundation\Auth\ResetsPasswords. But you don't want to edit this file. This file contain a php trait that use in PasswordController class.
So you can change the functionality of the trait methods by overriding it.
postEmail is the methods to be overwritten that find the user with given email and send reset link. Find the user by email case insensitively using ilike. Then overwrite request email variable by exact user email.
Following is to be the code in your PasswordController class (App\Http\Controllers\Auth\PasswordController)
public function postEmail(Request $request) {
$this->validate($request, ['email' => 'required|email']);
//Find the user by email case insensitively using ilike
$user = User::where('email', 'ilike', $request->email)->first();
// Overwrite request email variable by exact user email
$request->email = $user->email;
$response = Password::sendResetLink($request->only('email'), function (Message $message) {
$message->subject($this->getEmailSubject());
});
switch ($response) {
case Password::RESET_LINK_SENT:
return redirect()->back()->with('status', trans($response));
case Password::INVALID_USER:
return redirect()->back()->withErrors(['email' => trans($response)]);
}
}