The simplest way to do is via WLAN Groups.
Create all 3 WLAN first.
Right now all of the APs should fall under the group called "Default". Click on Edit and select the 2 SSID that you desire to broadcast.
Create one more WLAN Group and check all 3 SSID.
Next, go to Configure > Access Points > Edit the AP that you want all 3 SSID to be broadcasted. Check on Overwrite WLAN Group and select your newly create WLAN group. Remember to do it for 2.4Ghz and 5Ghz radio if your AP is dual band.
Click on "Ok" when you are done and there you go, the selected AP will broadcast 3 SSID instead of 2.