Forgot passcode

For an iPhone unavailable notice, see the instructions in If you see an iPhone or iPad unavailable message or Security Lockout screen - Apple Support

Step 1 from those instructions is:

1. From your device's Lock Screen, try to enter your passcode five times until the "[Device] Unavailable" screen appears and your device asks you to try again later.

From there proceed to step 2 in the instructions in the above Apple Support article.