If no-one spotted or objected to the turn when betting was made on it, then i'd leave that where it was.
Now that the mistake has been spotted, I'd tend to fix the immediate problem and push the 6 into the muck and flip the real river.
the danger is that you get accused of angle shooting:
'you probably spotted the mistake but didn't want to say anything because it helped you.' Or something similar.
I like the general rule of fixing what's just been spotted, but don't try to roll back the clock.
Edit : just like krw17 said
