We've moved your post, as the older thread was already marked as resolved. Your inability to change the nameservers may have several causes.
If it's a CCTLD, there may be certain nameserver requirements
The new nameservers provided are not valid
Your Domain Manager screen may be caching (try a private/incognito browsing window)
If you'll provide the domain name and a screenshot of the error you're seeing, our volunteers in this community may be able to help you resolve the problem. There are no current issues being reported at GoDaddy that would prevent this action.
TLH - GoDaddy | Community Moderator Supporting you at x.co/247support