I would print out your Biometrics appointment letter and try doing the walk-in either way. It's been 3 weeks already since your missed appointment. Not sure but they might deny your case, you need to go do the Biometrics ASAP.
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Self filed AOS │Apps Received By USCIS - 3/18/19
│Biometrics Done - 4/11/19
Interview Scheduled - 4/24/19│Interview Date - 5/31/19│AOS Approval - 5/31/19
Permanent Resident Card Received - 6/8/19