How to reset the touch ID Passcode

Try going to Settings app > Touch ID & Passcode > and in the fingerprints section, remove all the prints.

If you don't remember the passcode you will need to use one of the procedures in the following link, since you cannot get into Settings > Touch ID & Passcode without entering the passcode. Forgot passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

If you do know the passcode then you can go to Settings > Touch iD & Passcode and then select "Change Passcode."