I recently ran into an issue where I had to rebuild an APIC in our ACI Fabric, and needed to rebuild it entirely.
The procedure is pretty simple, and I had ssh access to the device, so was able to complete it very quickly, you can also run this from the rescue-user either via ssh or console if all else fails.
Run the following 3 commands:
- acidiag touch clean
- acidiag touch setup
- acidiag reboot
Upon reboot it will bring you directly into the Setup Utility and you can add it back to the ACI Fabric.
Official Documentation Source: https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-x/troubleshooting/b_APIC_Troubleshooting/b_APIC_Troubleshooting_chapter_01001.html