Welcome to Android Central! You can always do a factory reset -- that's usually the only way to get rid of the existing private space password and create another. But as belodion mentioned, all of the data on the phone (including what's in the private space) will be lost. You'd need to back up or sync all of your important data prior to the reset, and I'm not sure if that would also include the private space.
In addition, doing a factory reset also assumes you know the Google account and password that's associated with the phone, because if you don't, you'll run into Factory Reset Protection.