[Urgent help needed] Changing database user password won't let users login to the admin page of website

EDIT: My issue is solved. For some reason, one of the past maintainers of the website harcoded the login page and in the process, connected to the database (for no reason I might add, as the login process shouldn't be doing anything with literally any kind of database, it literally only takes them to a static dashboard page with effectively nothing on it) using the exact same details that I had changed and was using some strange function that would route the user input username/pass to check whether the hashed passwords matched, which would then go into a function which filled in the login/pass with the hardcoded username/pass and log you in that way. By changing the password, I had effectively broken this strange login process as it was trying to connect to the database using the old DB password stored in plaintext in a random .php file somewhere deep in the guts of the project. Guess it's time for a full rework of this website, to say the least. Hey all, Fairly (read: completely with 0 experience) new to cPanel, and relatively new to development itself. Currently working on a pretty old, messy website. What I did was change the password for one of the SQL users in the MySQL" Databases
(see this imgur link for picture of what I'm talking about) section, as the user doesn't remember what the DB password was. It didn't prompt me for any kind of current password or anything, which I found strange, but I assume it's because I'm already signed in. Note, this is the one and only thing I changed in the entire website. Now, I tried logging in to the user's website, in their example.com/admin section, however using the user's login details, I get this screen (imgur). Access denied for user 'v[REDACTED]9'@'localhost' (using password: NO)
Now, that username that I redacted is identical to the cPanel username I see in the top right of the cPanel navbar (imgur). If I go into the User Manager
section of cPanel, I again see this same user (obviously, since I assume this is what the root user is), however don't have the option of modifying anything about this user. I'm truly at a loss here, because I don't see a reason why changing the password for DB access would affect anything on the website login side of things, seeing as the cPanel username and the username of the person logging in are not the same. In fact, trying to login with any of the user accounts doesn't work, and shows me the same error message. I deeply appreciate any and all help I can get on this, for now I'm trying to return to one of the backups GoDaddy has made.