In Browser :
Open
https://cloudflare.webscoot.io/purgecache/your-domain.com
in browser.
When prompted for username and password enter the same.
Using cURL :
curl -u 'your-username:your-password'
https://cloudflare.webscoot.io/purgecache/your-domain.com
curl
https://your-username:your-password@cloudflare.webscoot.io/purgecache/your-domain.com
> e.g. URL : https://exampleuser:examplepassword@cloudflare.webscoot.io/purgecache/your-domain.com