Had to move the server to a new ip address. After moving it is impossible to configure a new target in the NSX-T manager
I manged to get the configuration option back. I needed to setup a new server with the same ip address and ssh/sftp enabled. Then NSX manager was able to edit the config again. This seems like a bug. You should be able to change the backup target/restore source when it is not availeble. vCenter can do this without issue.
this was good work round. but in NSX-V working good and can be changed. did you try to change it from the CLI.