Following steps show how to export NSM settings, using NSM included API Gateway.
Step 1: get the bearer token from NSM. Please refer the KB at the end of the article.
example token:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpc1RGQSI6ZmFsc2UsImlzVEZBQ29tcGxldGVkIjpmYWxzZSwic2Vzc2lvbklEIjoiMjEyMzJmMjk3YTU3YTVhNzQzODk0YTBlNGE4MDFmYzMtMTEwMDI2Njc5NDUzOTM1MzU2MyIsImV4cCI6MTY4NDI5NjM4OX0.2i183irP6A37O-gIKJhf_LTEzta-QJP5d_4l6icRz6E
Step 2: log into Postman, click "+" to add new collection. Give it a name like "NSM Export Settings":

Step 3: click on 3 dots to add request:

Step 4. change the name of the new request to something like "Export settings":

Step 5. enter URL to include "api/manager/system/settings/export" at the end of NSM URL, including port number. Then click "Save".
Example:
https://192.168.167.120:8443/api/manager/system/settings/export

Step 6. go to collection "NSM Export Settings"/"Authentication, select Type "Bearer Token":

Step 7. paste the token from Step 1 to the Token box, then save:

Step 8. go to "Export settings" request, select "Send and Download":

Step 9. save the output file:

KB on how to to get bearer token for API use: