When you get a Corn home, you should leave it absolutely alone for a week. No handling at all. First it has to settle into it's tank and start to feel safe in there. Make the process easier by giving him as many hides as possible at both the warm and cool ends - if they can hide away, they feel more secure.
After that, you can start gentle handling to try and persuade him that you're not actually a huge pink monster that wants to eat him (which is what he thinks at the moment!). Sometimes it can take a few weeks for them to be calm about being handled, so be very gentle and patient.
Also, try not to put him down if he nips. He'll soon figure out that he can make you let go that way and the habit can take a while to break. He needs to understand that nipping won't get him what he wants, so eventually he should stop bothering.
Also, do a quick double check that the temperature on the floor at the warm end isn't too high. That can make them very antsy and more liable to biting.