Practice cognitive behavioral therapy and specifically their cognitive distortions, eg fill in a “daily mood log” form (look it up). Reading about distortions propositionally is not going to get you better, you have to train yourself finding them in the context of your life. Turns out most of the time we are bummed there is a high chance of these biases being in play.
Honesty and a willingness to accept that you're just as biased as anyone else can get you pretty far. A reasonable enough test might be: do you believe anything to be true that you wish weren't true? If every explanation you adopt for every social ill, every natural phenomenon, every historical event neatly fits a model that generates no discomfort, do you think it's more likely that the world really is that way or that you're privileging particular explanations?
> Honesty and a willingness to accept that you're just as biased as anyone else can get you pretty far.
I am very confident that there is a phenomena whereby someone can do this, but that in doing so their mind is in a certain "mode" of some kind (abstract, for starters), but when the mind is in a different mode (discussion or arguing about object level ideas, culture war topics tend to work best), the knowledge that they formerly had becomes inaccessible, often even if reminded of it.
My armchair theory is that this plays a part in it (but there are surely other things going on):