Mate 10 Pro: I’ve forgotten my private space password

At this moment, the only way to reset the private space password is by factory resetting your phone. If you've your fingerprint associated with the password, you would still be able to access the private space using you fingerprint.

You should be able to delete the private space from the main space without knowing the password if you haven't hidden the PrivateSpace option from the main space. Go to Settings > Security & privacy > PrivateSpace > Trash button > Delete and enter your main space lock screen password to confirm.