Admin mode Command prompt execution of IPMIConfig should work for any recent server as @Thayron Arrais describes and it should be your first choice.
On X8/H8 Generation and older hardware it may not always succeed. In those cases, if you reflash the IPMI Firmware with the -C (clear config) option on the flash utility, even with the same version currently on the device, from an admin command prompt you can reset the IPMI configuration to its default settings.
On the older Systems that is ADMIN/ADMIN (in all CAPS). On systems produced after a California law on default passwords went into place, that password is printed on a labels attached to the Chassis Toe Tag, or the motherboard directly.
This method also works for clearing BIOS System and User passwords using the regular Firmware flash utility -- physical access is godmode as far as permissions go.
The BIOS lets you set an IP, once it is set, you are expected to do everything through the redfish webgui or various OS provided IPMI/i2C tools. If your system supports it I highly recommend enabling the dedicated remote management interface if your system has one. Don't use the failover interface mode for security reasons.