If your domain is registered with 123-reg, you can access your DNS Zone from your Domain name overview → DNS tab.
You can find detailed tutorials on creating, editing, and deleting DNS records at 123-reg here:
Hostinger default DNS records:
If you face any difficulties while managing DNS Zone at your domain provider, it’s best to contact 123-reg directly. Alternatively, you can transfer your domain to Hostinger so your hosting and domain will be managed from one place 😊