In that case, you will have to convert the IAP into a campus AP.
1.Connect the AP to a separate subnet so that it will come up as the virtual master and you can log into the web UI of the AP.
2. Maintenance -> Convert
Convert one of more Access Points t0:
Campus APs managed by a Mobility Controller
-> Enter IP address of the Mobility controller
-> Hit Convert Now.
You should see the AP come up on your controller.