First, if the main domain is not pointed to Hostinger, make sure to change the nameservers to those of Hostinger and then proceed. You can find more details about it here. You can also point it following a second method, which would be via A records, also stated in the article.
If the main domain is already registered at Hostinger or pointed to Hostinger, proceed to the next steps.
Navigate to the Websites list section on the left sidebar,
Click on Change domain for the specific web application that you wish to connect to your subdomain
Follow the next steps on the hPanel and add your subdomain:
You can also connect your subdomain inside Horizons editor. For that, follow these steps:
Click on the Publish button to prepare your website for going live:
Once your website is ready to publish, you'll see an option to Connect Domain. Click on the Get Domain button:
This will redirect you to the next screen where you’ll be able to enter the subdomain you want to use. Enter the name and follow the next steps inside hPanel.
How to get your web app online
After connecting your subdomain to the web app created with Horizons, in order to get your web application live, you need to publish your project.
To publish it, click on the Publish button in the top right corner of your Horizons tool:
When the publish is successfully completed, you will be presented with a unique generated link to view your new web app:
When the publish is successfully completed, your new web application is now live and ready to be used 🚀
You can find more details about publishing your project in this article.
You are unable to connect subdomains from another user inside different accounts, it will displayed as hosted by another user.