When running as a controller-based AP they typically get their IP address via DHCP. There is typically no need to statically assign the IP address.
If you need to hard -set the IPA connect to the console of the AP, reboot, break the boot process then use the setenv commands to set it: >setenv ipaddr <IPA., setenv netmask <mask>, setenv gatewayip <IPA>. All the setenv commands are listed in the AOS Users Guide.