How to disable or change a Hide My Email address?

Today I received a spam email from a company called Too Good To Go, and the From and To fields show email addresses ending with @privaterelay.appleid.com. I am not an iCloud+ user, and my iPhone and iPad are still on iOS or iPadOS 14. When I log in to icloud.com and find Hide My Email and select the Manage button, I get only an info screen that links to https://support.apple.com/kb/HT212519. How do I stop this address from forwarding to me? (The form interface for submitting this question requires me to choose a device, but this question is not device-specific.)