Ive never had to use softaculous i guess its cpanel pre-included auto installer?
If it is then you need to do a reinstall... I don't know of any auto installer that can add users, but i could be wrong... Theirs always a chance you can google to find a way for manual password change for wordpress if you don't want to reinstall...

Just to know if this is your first time getting hosting... You should learn to install scripts manually without the need of a autoinstaller because you will never learn to use better scripts since their are more better ones out there not on a autoinstaller.