When and if you register with AuthServ, you specify a password you want with that account. This has nothing to do with mIRC as a program, if you used a totally separate program to connect to the IRC network then your password would still be valid.
If you didn't receive a confirmation email, usually your account will expire aftr 24-48 hours, so your account may not exist anymore.
However, the best thing to do is to go to your network's #help channel, or other official help channel, and ask them to help you - as stated, a network's services are unique to the network and they are better qualified to help you. Check out the network's website too for online documents. If you don't know the website, search
Google.
Regards,