the screen capture doesn't really show it to be missing or not, it's outside of the region you screen captured. It should look like this
failing that, do it from the CLI
conf t
provision-ap
read-bootinfo ap-name <the ap name>
a-ant-gain XX
g-ant-gain YY
reprovision ap-name <the ap name>
!
!
dont forget to make sure master/remote-ap is set as required, which it should be if you are "reading" the boot info first as above.