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You need to apply to change your employer through the web site. You cannot directly work for the new employer without applying for the change of employment. Doing so will be working illegally.
 
Thank you for answering my question, do you know how long will it get approved? As soon as I apply online, I can work for the new employer, right? or do I need to get a new work permit?
 
I'm sorry - I don't know how long it will take.

You have to wait until you are approved before you can work for the new employer.