From my testNG installation note, you can refer.
The eclipse 2019-09 not support install TestNG from Eclipse Marketplace, so,
Install from update site
Select Eclipse Help / Install New Software...
Enter the update site URL in "Work with:" field:
Update site for release:
http://dl.bintray.com/testng-team/testng-eclipse-release/.
Make sure the check box next to URL is checked and click Next.
Eclipse will then guide you through the process.
after restart eclipse IDE, check Windows / Show Views / Java
Create new TestNG class.
Set TestNG debug configuration
show TestNG result.
Hope it can help you.