What is the procedure for reregistering an APX120 in CM?

Hello everyone,
Please guide me on how to reregister my APX120 in CM. My APX120 was deleted while I was trying to identify issues with my CM account. It is reliable advised that the issues have now been identified and will be resolved when v19.0 GA is released. Therefore, I have tried reregistering the APX120 in the CM wireless without success.
I have tried the following steps:

1/. power on APX120 and start registration process in CM - fail

2/. check XG115W is actually passing he APX120 traffic and it is.

3/. restarted the CM registration process then restarted the APX120 - fail.

4/. rhard eset APX120 and restarted CM registration process - fail

5/. found the reset APX120 now appears in the XG115W wireless tab.

6/. deleted the APX120 from the XG115w - restarted CM registration process - fail.

7/. APX120 continues to appear in the XG115w wireless tab.

In order to reregister the APX120, I'm looking for some hints