Apparently, one must use Revolut from a cell phone. There appears to be no way to use Revolut from a desktop machine.
But I cannot download the required App to my Android cell phone. I enter the cell phone number, but never receive the message with the download link
I tried calling what I thought was customer support at +44-203-322-8352, but this was a waste of time since according to the message I got, this number is exclusively for canceling a card.