I forgot my iPhone's passcode

If you forgot your iPhone passcode, you'll need to erase the device and restore it from a backup. You can do this by connecting your iPhone to a computer with iTunes, using Recovery Mode, or through iCloud's Find My iPhone feature. After erasing, you can restore your data from a backup if available.

connect it to a computer using the cable and read

If you forgot your iPhone passcode, use your Mac or PC to reset it - Apple Support