The only way to fix this is for it to be a lie meant to bring about the Valeyard... somehow.
One thing I want to say is that I don't think many people realize how cold and calculated this move was.
I mean they gave zero fucks about canon, but politically
they did give it A LOT of thought and used some dirty tricks to make this stick.
They knew the Doctor Ruth thing was risky, so Chibnall brought Captain Jack, and the Judoon, in the exact same episode.
That wasn't a coincidence. This was actually a trap for people that were around the 9 and 10 doctor eras.
You can't question the canonicity of Ruth and this episode, without also rejecting Jack's cameo because it's part of the whole.
The fact that Chibnall did the timeless child retcon in the last episode of the season was also a dirty trick. You see, Chibnall is playing the long game here.
It's not a coincidence there is a huge hiatus until Christmas/New Year. And
neither is it a coincidence that The season finale ended with the doctor accepting the reveal quickly and moving on to an unrelated prison break episode as if nothing had happened.
Chibnall and the BBC are betting in that all the complaints will die out during the hiatus as people will inevitably stop talking about Doctor who once something else like the MCU gets people's minds away. If Chibnall is smart, and he isn't, most likely, the next episode won't mention the retcon at all to give more time to people to shallowing it in.
Once sufficient talk has passed, they will bring the retcon back hoping people will have just accepted it.
Had the retcon being in any episode, but the finale, the backlash and rating drop would've been huge, and they know it. That's why it happened at the very end. There's no way for the fans to retaliate that will affect them directly until, after, they hope people will have moved on.
There's also the usual dirty tricks: Retconning the pre-Hartnell doctors would also mean getting rid of Ruth, aka, the "first female black doctor", and you can expect racism accusations for anyone that tries.
I hope this plan of theirs fails. But tbh on my end, I'm done with the show unless they retcon this.