What if someone used old software or wanted to change KSK manually and failed? In that case, the DNS Resverver will stop working so anyone at the end of the connection will not be able to access the website they want. They can of course find their own way but it will take a lot of effort.
Internet infrastructure companies are also aware of the problem and plan the transition for months. But for system administrators, operating Resolver, developing DNS software or those who install Anchor Trust on Root as part of software or hardware and are worried about this conversion, ICANN has a test page KSK https://automated-ksk-test.research.icann.org/ and an information page for you to read. https://www.icann.org/resources/pages/ksk-rollover