If your domain is registered with IONOS, you can access your DNS Zone from your DNS Settings section while logged in here.
You can find detailed tutorials on creating, editing, and deleting DNS records at IONOS here:
Hostinger default DNS records:
If you face any difficulties while managing DNS Zone at your domain provider, it’s best to contact IONOS directly. Alternatively, you can transfer your domain to Hostinger so your hosting and domain will be managed from one place 😊