Pretty nebulous question dude - experiment! plus what the other guy said about time and patience to mature up.

Many many options and these are just some off the top of my head...

1. 5http or L-tryptphan
2. Vitamin B6/1 with above (sometimes Niacin and Thiamine helps with it)
3. Adaptil (a pheromone spray that mimicks their mumś calming scent when they fed as puppies)
4. A compression suit
5. Reconcile (dog version of prozac - it swabs and cannot be used in competition but it can help a struggling dog adjust and settle in)
6. Sometimes and rather counter-intuitively a stimulant like caffeine/No-Doz will help sharpen a young dog up and make it more mentally acute and confident. With this one they either respond very very well or go backwards, wouldnt take long at all to know whether it is helping or hurting. Again used in moderation and outside of competition.
7. Sometimes (if the dog likes you and is confident with you as its owner) it is as simple as one of your old shirts or clothing... but you have to wear it like three days without washing it then give it to them as part of their bedding. It's because the dog has bonded to you and you are now it's mother. It's a replacement strategy to the adaptil if they were taken from mum too soon or forgot about her during rearing.
8. Mixtures and combinations of all the above

That's a starting point and in my personal experience 8/10 can get it out of them and the residual 20% seriously just have coping disorders that I never found a solution too other than retirement to become a pet.

Hope it helps for ideas and things to try anyway. It's a truly rewarding feeling when you can get a nervous/anxiety ridden pup to focus and run. To me that's a more rewarding feeling than any prize money on offer.