TriggerFinger - by default the appliance should get a DHCP address, which you can use initially to connect to the web UI. Then via the web UI, you can set up a static IP. From the product documentation:
Automatically Acquired IP Address: DHCP is enabled by default on the ExtraHop appliance, so when you power on the system, interface 1 attempts to acquire an IP address using DHCP. After the DHCP server assigns an IP address, the ExtraHop system displays it on the LCD at the front of the appliance.
Static IP Address (CLI): If your network does not support DHCP, you can use the ExtraHop web administration utility or the command line interface (CLI) to configure a static IP address. You can access the CLI from a USB keyboard and SVGA monitor or by using an RS-232 serial cable and a terminal-emulator program. The terminal emulator must be set to 115200 bps with 8 data bits, no parity, and 1 stop bit (8N1). Hardware flow control should be disabled.
If DHCP doesn’t work you can connect a RS-232 serial cable to a laptop/server in your data center and then use a terminal emulator program (minicom, putty, etc.) on that computer to access the Extrahop CLI. Then from the CLI you can configure the static IP.
More details at https://docs.extrahop.com/current/install-eh6100-8100-9100/