Locate to TexturePacker App, it is usualy in the Applications folder. Right click on file -> `show content'
Go to:
/Contents/Resources/exporters
copy and paste the folder unity-ngui inside.
https://www.codeandweb.com/texturepacker/custom-exporter/extend-exporter https://www.codeandweb.com/texturepacker/documentation#customization