Intallation not finished

I try to install nextcloudpi on my Raspberry Pi somehow it seems finished and I rebooted the RPI. When I enter the IP address, I get a sign in page:

But I didn’t register anything. When I try to run the installation script again
( curl -sSL … | bash) then it says

WARNING: existing mysqld configuration will be changed <<<
The ‘nextcloud’ database already exists. Aborting

How can I restart the installation or how can I register myself to nextcloudpi?

When you install ncp and first access the IP address the credentials are shown. If you reboot without saving them it gets difficult.
A possible way is to access the machine with root an enter ncp-config there you can change the passwords manually