First of all, your domain is not assigned to any hosting account. You must do this first or our servers won’t know which website to show on it:
However, to do so, you must change the nameservers of your domain first. Which you cannot do, because the domain is registered with Cloudflare, and they don’t allow this.
Please consider transferring your domain name to a registrar that does support setting custom nameservers, so you can add the domain to your account.
After that, you’re free to switch back to Cloudflare’s DNS service if you want. You can follow this guide for details: