unlock phone if I don't know 6 digit pass code

You will need to restore the phone using a computer. The process will erase the device. Later you can restore your data from a recent back-up. Instructions here....

If you forgot the passcode on your iPhone, or your iPhone is disabled - Apple Support

You can reset your password using this steps but you'll need to have a back up in order to restore all your data https://support.apple.com/en-us/HT204306