1&1 install 404 error

I cannot find any reference to WordPress on that domain. Check where you uploaded the files to.

The issue with 1&1 is that php version is outdated so WP wont run the install. You need to add some hacks in your root folder like php.ini or htaccess so it bypasses it.

Is there a link or can you explain to me on how to do so?

Not sure how your server is setup but you can try this link for all php versions
https://php.net/releases/index.php

Try asking your hosts for assistance with this.