Your account is the login you sign in with; the server mints it the first time that login arrives and is the only side that decides what it owns. Every sign-in goes through the provider's own page - the game never sees a password. Link Account joins a second login to the same climb; Reset Progress and Delete Account live beside it.
1Pick a provider
The sign-in gate shows one button per provider the server has configured - Steam always; Google and Discord now; Apple the day its key is set. In the Steam client there is no gate: the shell signs you in with your Steam session.
2Account & Data
GAME SETTINGS > ACCOUNT & DATA holds your account: Sign Out, your player name, Link Account, Cloud Save, Export My Data, and in red Reset Progress and Delete Account.
3Link a second login
Link Account signs you in to this same climb with another provider - Steam on the desktop, Google on the phone - so one account carries both. The link is permanent and the name stays yours.
4Reset or delete
Reset Progress (New Game) wipes this save and starts at floor 1 - the account, its name and its badges stay. Delete Account removes the account seven days after you confirm; signing in before then cancels it. Both ask you to type the word before they act.
Screenshots are taken from the live game by tools/tutorial_shots_b.py (dfmc-client) and regenerated after interface changes. The rules behind each screen: system-accounts.