To change the nameservers for your .de domain, make sure that it is added to your hosting plan: How to Add a Website. This will ensure that your domain has an active DNS zone, which is a basic requirement for the modification.

Once your domain is added to your hosting plan, access Denic.de website and enter the domain name and nameservers you wish to specify.

For Hostinger, they are as follows:

ns1.dns-parking.com = 162.159.24.201
ns2.dns-parking.com = 162.159.25.42

Everything should be green:

In case an error appears, you can check the meaning of each error code here.

After that, your domain will take up to 24 hours to point, though it usually takes only a few hours. You will be able to monitor it live via dnschecker.org 😊