The only way is excercing and practice.

The problem usually I find is that the harder you try the harder it gets and the more frustrated you get and worse you feel.

Play what you can do without problems then have 10 minutes practice with the difficult pinky problem.

Then play something you find easy again.

By doing this you start out feeling good as you play, then you practice the hard stuff and feel a little frustrated and then you finish again feeling good about the last peice.

Then rest, have a drink and a little time to unwind then after about 10 minutes begin again.

Try noy to over practice at first and try not to let it eat you up.

This is how I have over the years overcome those parts and tricks I struggled with.

Never beat yourself up over what you have not yet acheived
but instead think how far you have come and what you have acheived sor far, this may be waht is needed.

I hope this is of use, frustration can be our worst enemy.