Forgot passcode

There is an Apple article that explains what to do if you have forgotten an iPhone or iPad passcode. Click on the following link: How to remove your iPhone, iPad, or iPod touch passcode without a computer - Apple Support

If that option is not available, you will need to use a computer. See: If you forgot your iPhone passcode - Apple Support

You cannot change a passcode through a trusted device (or any other way). You need to restore the phone to factory settings, then restore your backup.