unable to fetch existing credential due to error -25291

Hi Roman_Sam,

Welcome to Apple Support Communities and congratulations on your new MacBook!

We understand that you're seeing an alert when you're attempting to set up your new MacBook.

The error -25291 is generally related to network issues affecting your connection to Apple's servers that may have to do with a proxy server or network firewall, for example.

So that we can help isolate this behavior further, are you connected to a Wi-Fi network or is your MacBook connected directly to your modem or router? Are you able to complete installing if you switch your connection? Where are you seeing this alert? Are you in macOS Recovery mode when you see this alert?

If you're using Time Machine to restore your files, you may consider starting in macOS Recovery to restore your data. You can learn more here: Use macOS Recovery on an Intel-based Mac - Apple Support

Use Time Machine to restore your system

If you previously created a Time Machine backup, you can restore everything on your computer to its previous condition.

Important: Only use your Time Machine backup to restore information to the computer that is the source of the backup. If you want to transfer information from this Mac to a new computer, quit macOS Recovery, restart your Mac, then use the Migration Assistant app in macOS.

1. If your backup is on a Time Capsule, make sure you’re connected to the internet.

2. In the Recovery app, select Restore From Time Machine, then click Continue.

3. In the Time Machine System Restore app, follow the onscreen instructions.

We look forward to your reply.

Cheers!