HTC Desire 20 pro User Manual page 53

53 Phone calls
5. Select or clear the Report call as spam option, depending on whether you want to mark the
number as a spam call.
6. Tap Block.
§ To unblock a number, press and hold the number, and then tap Unblock.
§ To see and manage your list of blocked phone numbers, tap
On the Blocked numbers screen, you can also turn on the Unknown On/Off switch to
automatically block calls without caller IDs.
Settings Blocked numbers.