Unfortunately, you can’t fix it - it will require a DH admin to update the library. They are aware of the issue, but feel to free to contact support as a “reminder” if you wish; it can’t hurt.
That warning should not be impacting your ability to modify databases; I’ve done major work via phpMyAdmin without error in spite of that message for a while now.
If your user is being denied there must be a credentials issue. I suggest you re-check the DH control panel information for the database in question to make sure your db user, db user password, and MySQL hostname are being entered correctly.