There is no need to reconfigure Ubuntu, but, if you have more than one distribution installed and Ubuntu is not your default, you must also specify the distribution in addition to the root user.
Then go about your business to reset your regular user account. Stealing the one-liner from @NotTheDr01ds, assuming your distribution name is "Ubuntu":
wsl.exe -d Ubuntu -u root passwd username
Typical Ubuntu distribution names include:
- Ubuntu: When installed from the Microsoft Store or
wsl --install as the "unversioned" app.
- Ubuntu-18.04, Ubuntu-20.04, or Ubuntu-22.04: When installed from the Microsoft Store or
wsl --install as a specific version of Ubuntu.