If you have APs on either a standalone controller or that are registered locally to one of two controllers in a High Availability pairing, and you need to "move" them from being registered locally on the controller's they are currently registered with to a new/different controller, you can do that easily using the Multi-Edit function.
Step 1. Be sure the controller you want to move the APs to, has A.) licenses enough available to allow all the APs you intend to move to be registered there, in place and active and B.) that it has the "Allow All Wireless APs to Connect" option enabled under AP > Global > AP Registration and C.) that it has a port of type "Physical" created and accessible for the APs in question over the L2/L3 path that lies between them and that port with "AP Registration" enabled
Step 2. Back up all controllers involved before making any changes
Step 3. Export the AP Inventory report on the "original" controller so you have a safe-guard copy of all the names of all APs and their corresponding serial numbers for reference should that be needed later
Step 4. On the controller you want to move APs from, navigate to AP > APs and select all APs that you want to move from that controller, to be registered to a new/different controller, and when you have the desired APs selected, choose "Multi-Edit" from the list of available Actions from the "Actions" drop down list (see below):
Step 5. Scroll to the very bottom of the Multi-Edit screen
Step 6. From the "EWC Search List" Drop Down menu, select "Reconfigure Search List" (see below):
Step 7. Click on the "Add" button from the EWC Search List / Reconfigure Search List" screen presented, and add the IP address of the controller you wish to have the APs you have selected previously moved to and registered to as "Local". If you are moving APs to be part of a High Availability Pair ... you can also add a second IP address to add that 2nd controller IP address as "Foreign" for the APs in question.. If you make mistakes or need to re-order the IP addresses for any reason, you may use the "Up", "Down" and "Delete" buttons if necessary.
Once you have successfully populated the search list to your needs, click the "Apply" button.
Step 8. Reboot all the APs that you are trying to move, either using Multi-Edit again and selecting the "Reboot" action, or by disabling then re-enabling PoE power to all the AP ports in question
Step 9. Re-Select all the APs on the original controller that you are moving to a new/different controller and click the "Delete" button in the bottom right hand corner to remove them from that controller
Step 10. Allow enough time for the APs in question to fully reboot and after such time has elapsed, you should see those APs having moved to your new controller. If the names of the APs have been "lost" that is because they are newly registered on the controller you moved them to and have never had a "name" on that controller. In that case, you can refer to the AP Inventory Report you exported from the "destination" controller ... and match up serial numbers to AP names to be able to rename the APs on their new controller(s).