If you've started creating your website on Hostinger Webiste Builder and would like to use WordPress (or another CMS) instead of Hostinger Website Builder, you simply need to delete the website built with the builder in order to release your domain name.
Before deleting a website created with Hostinger Website Builder, you can export website files
A deleted website cannot be restored
If you have an email service set up for your domain, make sure to create a backup of your emails, as deleting the website will also delete emails
In hPanel → Websites, delete the website that you've created:
Create a new website and choose WordPress (or another CMS) as your preferred website-building platform:
Click Create or migrate a website
Select Build a website
Choose WordPress (or another CMS)
If you select WordPress, to finish the setup, create a WordPress account, choose the preferred plugins and website template, and insert the domain name that you've previously released by deleting the website built with Hostinger Website Builder.