Deleting your Wordo account removes your account, your words, your digests and your device registrations immediately. There is no waiting period and nothing is kept.
Sign in, open Settings, scroll to Delete your account and confirm. The Android app and wordo.io have the same button.
Write to contact@wordo.io from the email address of your account, asking for it to be deleted. It is done by hand, usually within a few days, and confirmed by reply.