First, you’ll need to get SSH access to your server: https://tran-technology.com/how-to-ssh-or-sftp-into-your-unifi-server/
Log in via SSH, then use wget to download the script from GitHub:
Customize -u, -p, and -e inputs to provide the username, password, and email address for the new Super Admin account. Run the script:
You can now log in to your UniFi server with the new Super Admin!