Go to the Blocked List and tap the "+" in the top left corner. Key in the number using the keypad.
Or add a number from the Lookup tab by swiping the number right and choosing 'Block'. You can also add a number to the Blocked List on the number details screen of a looked up number.
Please allow up to 30 minutes for any changes to take affect on your iPhone.
Please note the Blocked List feature is only available to TPS Protect subscribed users.