I just downloaded and installed PhPList in a sub-folder on a sub-domain (adding these details in case it matters).
I used the default config setting details from config.
In trying to log in I always get “incorrect password”
I have reset the password twice and am still unable to login.
What version of phpList have you installed please?
What version of PHP is your server running?
Where have you added the sub folder on a sub domain details?
If all these details, and your password, are correct, try using phpMyAdmin to access your database and enter a simple password for your username and save, then see if that works.