For $29/mo, we provide access to advanced level technicians who will answer your questions on any Macbook board related matter to the best of their knowledge promptly & walk you through how to solve your problem so you can deliver a working board to your customer.
Do not even think about fixing something like this, it will destroy the LCD assembly.
if the coating were coming off the LCD you could take it to Apple. They will replace the display under the "retina stain gate" quality program for free.
Just live with the crack or if the customer is prepared to pay $400 (I bet not) go ahead and mess with it. If it all fucks up you can still go and get a new assembly.