Whenever my putting starts going bad, which is regularly, I go back to some basics a pro gave me. I break out the Eyeline mirror and makes sure I'm setting up decently. I tend to start setting up with my eyes way inside the ball.
I practice pushing putts to the hole. No hit, you just push them. It usually starts in frustrating as I miss the first half dozen left and then a few right before finally pushing them into the hole.
Then I break out the thin metal yardstick and start putting balls on that. I'll sometimes put something behind my putter to limit my backstroke. After all that my putting comes back.