GUI :
Select the AP-Group your AP is in or seach for the ap-name or ip-address and then pick the AP you want to make the change and click on provision
Under the IP settings you can define the IP address you want to assign to that AP
CLI:
(controller) (config) #provision-ap
(controller) (AP provisioning) #read-bootinfo ap-name <ap-name> or wired-mac <wired-mac>
(controller) (AP provisioning) #ipaddr <ip-address you are going to assign>
NOTE: For cert RAP; ap-name (if specified) in RAP whitelist entry will take the highest preference ( you can ignore this if this is not a Remote AP)
(controller) (AP provisioning) #reprovision ap-name <ap-name> or wired-mac <wired-mac>
Hope this helps