One way could be by using a VPN service, but it's not guaranteed to work and may also have legal implications. Another option is to create a secondary account with no identifying information, but this still doesn't ensure complete anonymity.
You can use some third-party apps, but be careful as they might violate Instagram's terms of service.
I'm not sure if there's a completely safe and legal way to view Instagram stories anonymously. Usually, Instagram has security measures in place to prevent such activities. It's best to abide by the platform's rules and use it within the intended guidelines.