Email us
Tell us what you were doing and what happened instead. A screenshot of the screen you were on is usually enough.
What to include
The email address you sign in with, and — from More → About SET in the app — the version, the environment and the device it names. Those four tell us which copy of SET you are on.
If you cannot sign in
Email us from the address on the account. Nobody at SET can read your password, so getting back in starts with confirming the address rather than recovering the old one.
Something a customer of yours saw
Send the link they opened along with it. A customer's page is reached by a link of its own, and having the exact one is the difference between us guessing and us looking.