How to update forgotten password on iPhone 8 if PC doesn’t recognize it?

Try to to it without a computer

If you're using an eSIM on iOS 16 or earlier, contact your carrier before trying these steps and ask for a QR code to set up your eSIM again. 

1. From your device's Lock Screen, try to enter your passcode until the "[Device] Unavailable" screen appears. 
2. When you're able to, tap Forgot Passcode?
3. On the Security Lockout screen, tap Start [Device] Reset to confirm. You can only reach the Security Lockout screen if you have an active cellular or Wi-Fi connection and previously enabled Find My on your device.
4. Enter your Apple Account password to sign out of your Apple Account on your device.
5. Tap Erase [Device] to permanently delete all of your data and settings. If you use an eSIM with iOS 17 or later, you can also choose to keep your eSIM and erase your data, or to delete your eSIM and erase your data.

6. When your device restarts, follow the onscreen instructions to set up your device again, restore your data and setting from a backup if you have one, and set a new passcode.

If you can't follow these steps, you can use a computer to reset your device.

You said your computer didn't see your iPhone. See if this helps --> If your computer doesn't recognize your iPhone or iPad - Apple Support

Then do as LD150 suggests and use a friends computer or visit your closest Apple Store Genius Bar for help.

yakhontova wrote:

My PC DOESN’t see iPhone through USB

Borrow one.