50 amp plug on 30 amp circuit for dryer
There should be either a NEMA 10-30R, or 14-30R receptacle where your dryer will plug in.


NEMA 10-30R


NEMA 14-30R

When you purchase an electric dryer, the store should also sell you a cord for the dryer.  Most times they'll ask you which you need, or they'll just have both on hand if they're installing the dryer for you.

If the installers (or you) simply installed the wrong cord, you should just be able to replace the cord with the proper one. You'll need to install either a NEMA 10-30P 3-wire cord, or NEMA 14-30P 4-wire cord depending on which receptacle is in your home. 

If for some reason the dryer requires 50 amperes, instead of 30. You'll have to replace the breaker, the wiring from the breaker to the receptacle, and the receptacle.

If there's a NEMA 10-50R, or 14-50R receptacle installed in the home on a 30 ampere circuit. You should replace the receptacle with the proper one. Receptacles and plugs are configured in different ways, to prevent things from being plugged into an undersized (incorrectly sized) circuit.