How to reset unavailable iphone without computer

Hello,

Go to any Apple retail outlet or service provider:

Find Locations

Alternatively, do you have a Best Buy location or something similar nearby? They also would be able to help.

For more detail:

If you forgot your iPhone passcode - Apple Support

Good luck.

Hi,

Please follow the steps from the link

If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

If you are unable to erase your device after following the steps from the above link, you can also try to erase your device remotely from find my.

From any device, open browser and go to iCloud.com/find and sign-in with your Apple ID. Then select your device from the list of Devices and choose erase iPhone. It will erase your device remotely.

Did you try the steps in here?

If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support