Display of error message

Hello,

I am using this multi-step plugin and I want to make changes to error message. If I enter the ZIP code wrong in billing address then I get error message ‘Billing ZIP is not a valid postcode / ZIP’ on placing order i.e in the last step. But on making correction to the ZIP and when moved to next step the error message remains the same . It does not disappear. How to make this work. And also how to move to in-between step in multiple step i.e how to move directly to billing address from place order form without clicking prev button and also vice-versa. Thanks in advance.