One of two things is happening here. Either there's a glitch in the system not allowing you to see the "change" button or you may be having some caching issues.
First thing I'd do is clear my browser cache and see if the button comes back. If not...
Call support and have them take a look. It may be something internal they can fix or at least give you some advice on.
You could also go to the DNS management system for wherever you have the nameservers currently and put them back to GoDaddy nameservers. You may have to call their support for help with that.
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