If I'm having trouble with something...
Let's say making a quick leap with my left hand to reach a low C, and I keep missing it.
I'll play it 20-30 times in a row slowly and accurately. Then, I'll leave it alone.
After a decent night's sleep, it's always better the next day.
If the accuracy is still a little questionable, I'll do the same thing. 20-30 times slowly and accurately.
Decent sleep. Next day. Even better.
I've come to see it like baking a cake (or other desert of choice). You have to feed the oven the right proportions of the right ingredients at the right temperature. And then you have to wait.
But you can't will a cake to bake faster. And you can't get better at heating a cake. You only get better at preparing the ingredients that go in.
Practicing like this, the challenge is always patience, of course. But, the exciting part is thinking about what it will feel like the next day.
And so, this has become my routine when I need to fix things in my playing. Sure, there's that first moment of panic. The "How does anyone play this?!?" moment.
But every time I get the slow, accurate reps in, it feels more possible the next day.
Again, just like baking a cake.
So long as you start with the right ingredients.