How can I reset my iPhone 6 passcode without computer

Dear Jason-94,

I’m afraid that you do need a computer to restore your IPhone and for the back up, to help you with this kindly check the following link which has a clear guideline how to do this process “https://support.apple.com/en-us/HT204306”

I hope that will helps

you don't a computer with itunes on it is needed to restore your device to factory settings.