Can’t set Apple Watch passcode

Hi there Justpanchenko,

Welcome to Apple Support Communities. To resolve this trouble you're having, first you will need to erase the Apple Watch Ultra completely. Follow these steps to do so:

"Erase Apple Watch Ultra and settings

1. Open the Settings app  on your Apple Watch Ultra.
2. Go to General > Reset, tap Erase All Content and Settings, then enter your passcode.
3. If you have an Apple Watch Ultra with a cellular plan, you’re offered two options—Erase All and Erase All & Keep Plan. To completely erase your Apple Watch Ultra, choose Erase All. If you want to erase and then restore it with your cellular plan in place, choose Erase All & Keep Plan.

You can also open the Apple Watch app on your iPhone, tap My Watch, go to General > Reset, then tap Erase Apple Watch Content and Settings.

If you can’t access the Settings app on your Apple Watch Ultra because you’ve forgotten your passcode, put your Apple Watch Ultra on its charger, then press and hold the side button until the sliders appear. Press and hold the Digital Crown, then tap Reset."

Complete details are found here: Erase Apple Watch Ultra - Apple Support

Once the Watch is erased, set it up again using the instructions from the Apple Support article:

Set up your Apple Watch - Apple Support

Step #6 guides you through setting up a passcode for your Apple Watch Ultra. Let us know if you have any questions.

We hope this helps you.