Seeing the 'I found a job' button does NOT mean that you have found employment thru Vivian. All Vivian users have this button visible in the Home page of their app, and it gives you the ability to report a job when you have already taken an assignment.
If you previously clicked on the I'm still searching button, you will see a check-in reminder and that button should now read 'Update reminder'. Setting a date for your next check-in just means that the app will send you a reminder to add a job in either 1 week, 1 month or 3 months. If you haven't secured a contract by then, the reminder will expire and no further action is needed.