A few more steps...
iOS 13/iPadOS beta profile has started downloading.
Make sure you open BetaProfiles.com in Safari browser.
You will see the following prompt:
Tap Allow from the popup
Then follow the prompts to install configuration beta in Settings app and restart your device.
After your device has restarted, you can receive beta update in Settings - General - Software Update.
You only need to install the beta profile once, the next updates will appear in the Settings app - General - Software Update.