Two ways to do it. Both end in the same place.
If you signed in a while ago, the app may ask you to sign out and sign back in first before it will delete the account. That's a security check, so that a forgotten unlocked phone can't be used to delete someone's account.
Email support@fayder.net from the address on your account, with "Delete my account" in the subject line and your username in the body. We use the fact that the email comes from your registered address to confirm it's really you, and we'll confirm in writing when it's done.
This happens immediately when you delete from inside the app, or within 30 days of an emailed request. Encrypted backups roll off on their own within 90 days.
Deleting is permanent. There's no undo and no way to get your posting history back. If you just want a break, you can make your profile private instead and leave the account in place.
Anything else, or if you'd like a copy of your data before you go: support@fayder.net. The full privacy policy has more detail.